WO2017095151A1 - Cathode for secondary battery and secondary battery comprising same - Google Patents

Cathode for secondary battery and secondary battery comprising same Download PDF

Info

Publication number
WO2017095151A1
WO2017095151A1 PCT/KR2016/014002 KR2016014002W WO2017095151A1 WO 2017095151 A1 WO2017095151 A1 WO 2017095151A1 KR 2016014002 W KR2016014002 W KR 2016014002W WO 2017095151 A1 WO2017095151 A1 WO 2017095151A1
Authority
WO
WIPO (PCT)
Prior art keywords
positive electrode
active material
material layer
conductive layer
electrode active
Prior art date
Application number
PCT/KR2016/014002
Other languages
French (fr)
Korean (ko)
Inventor
최영근
김효식
백주열
오송택
Original Assignee
주식회사 엘지화학
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 주식회사 엘지화학 filed Critical 주식회사 엘지화학
Priority to CN201680052380.0A priority Critical patent/CN108028355B/en
Priority to US15/754,479 priority patent/US11196051B2/en
Priority to EP16871047.3A priority patent/EP3370279B1/en
Priority to JP2018509517A priority patent/JP6620221B2/en
Priority claimed from KR1020160161525A external-priority patent/KR101938237B1/en
Publication of WO2017095151A1 publication Critical patent/WO2017095151A1/en

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a secondary battery positive electrode and a secondary battery including the same, which can improve the output characteristics of the battery by reducing the charge transfer resistance by the formation of an electrical network across the positive electrode.
  • lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used.
  • the lithium secondary battery includes lithium ions in an electrode assembly having a microporous separator interposed between a positive electrode including a positive electrode active material capable of occluding and releasing lithium ions and a negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions.
  • Nonaqueous electrolyte a material having conductivity by itself, such as a lithium metal, an alloy with a lithium metal, a carbon-based material, and the like is used.
  • As the positive electrode active material lithium cobalt oxide (LiCoO 2 ) and lithium manganese oxide are used. Transition metal oxides such as (LiMn 2 O 4 ) or lithium nickel oxide (LiNiO 2 ), and composite oxides in which some of these transition metals are substituted with other transition metals are mainly used.
  • the cathode active material has low electrical conductivity
  • a conductive material having high electrical conductivity must be included in the production of the cathode.
  • a positive electrode is prepared by applying a positive electrode active material composition prepared by mixing a positive electrode active material, a conductive material, and optionally a binder and the like as a dispersant in a batch to a positive electrode current collector and then drying.
  • the positive electrode active material, the conductive material, and the like are usually used in powder form, when mixed and mixed in a solvent, the compatibility with the solvent is low, so that the positive electrode active material and the conductive material are dispersed unevenly in the positive electrode active material composition.
  • the positive electrode active material composition in which the positive electrode active material and the conductive material are uniformly dispersed in the positive electrode current collector is formed on the positive electrode current collector, it is difficult to uniformly apply the positive electrode current collector to the positive electrode current collector.
  • a cathode active material layer having low uniformity or surface defects is formed, thereby degrading battery performance and lifespan characteristics.
  • the conductive material is used as fine particles of several tens of nm level, the cohesive force is strong, and aggregation between the conductive material fine particles is likely to occur when dispersed in a solvent.
  • the effect of improving the conductivity in the positive electrode active material layer is insufficient, thereby lowering the output characteristics of the battery.
  • the electrode when the electrode is manufactured using the conductive material, since the content of solids in the positive electrode mixture is higher than when the conductive material is not used, migration of the binder in the electrode occurs. Due to the migration of the binder, a nonuniformity occurs in the adhesive strength of the positive electrode active material layer to the positive electrode current collector during the production of the positive electrode, and as a result, the positive electrode active material layer is separated from the positive electrode current collector and peeled off. In this case, not only the performance of the battery itself is significantly lowered, but also the shortening of the battery life characteristics.
  • the first technical problem to be solved by the present invention is a positive electrode for a secondary battery, the charge transfer resistance is reduced by the electrical network across the positive electrode, and the output characteristics of the battery is improved by reducing the material resistance through porosity control in the positive electrode
  • the purpose is to provide.
  • a second technical problem to be solved by the present invention is to provide a method for manufacturing the secondary battery positive electrode.
  • another object of the present invention is to provide a lithium secondary battery, a battery module and a battery pack including the secondary battery positive electrode.
  • a porous positive electrode active material layer comprising a positive electrode active material and a first carbon nanotube
  • the cathode active material layer comprises a conductive layer located on the surface
  • the conductive layer includes a porous network structure formed by a plurality of second carbon nanotubes, and has a porosity of a positive electrode active material layer + porosity of 10% by volume or more.
  • the porosity of the porous cathode active material layer is 10% by volume to 50% by volume, and the porosity of the conductive layer may have a porosity of 20% by volume to 60% by volume.
  • the second carbon nanotube film is formed on the surface of the cathode active material layer.
  • a lithium secondary battery, a battery module, and a battery pack including the positive electrode are provided.
  • the secondary battery positive electrode according to the present invention forms an electrical network over the inside and the surface of the positive electrode active material layer using carbon nanotubes having strength characteristics along with excellent electrical conductivity, thereby maintaining a low material resistance in the active material layer while maintaining a charge transfer resistance. Can be greatly reduced, and as a result, the output characteristics of the battery can be significantly improved.
  • FIG. 1A is a schematic diagram schematically showing a cross-sectional structure of a positive electrode according to an embodiment of the present invention.
  • 1B is a plan view schematically illustrating the anode surface.
  • 2A is a schematic diagram schematically showing the cross-sectional structure of a positive electrode manufactured using a conventional fibrous conductive material.
  • Figure 2b is a plan view schematically showing a conventional anode surface.
  • FIG. 3 is a flow chart schematically showing a manufacturing process of a positive electrode according to an embodiment of the present invention.
  • Figure 4 is an electron microscope (SEM) picture of the surface of the anode according to an embodiment of the present invention.
  • Figure 5 is an electron microscope (SEM) picture of the surface of the anode coated with a conventional conductive material layer.
  • a secondary battery positive electrode according to an embodiment of the present invention is a secondary battery positive electrode according to an embodiment of the present invention.
  • a porous positive electrode active material layer comprising a positive electrode active material and a first carbon nanotube
  • the cathode active material layer comprises a conductive layer located on the surface
  • the conductive layer includes a porous network structure formed by a plurality of second carbon nanotubes, and has a porosity of a positive electrode active material layer + a porosity of 10% by volume or more.
  • the porosity of the porous cathode active material layer is 10% by volume to 50% by volume, and the porosity of the conductive layer may have a porosity of 20% by volume to 60% by volume.
  • the secondary battery positive electrode according to the embodiment of the present invention forms an electrical network by the first and second carbon nanotubes on the inside and the surface of the positive electrode active material layer, thereby greatly reducing the charge transfer resistance in the active material layer.
  • the porosity in the positive electrode active material layer and the conductive layer is converted into volume based on the true density of the sample of 25 cm 2 area measured using a pycnometer, and by rolling the electrode to a thickness corresponding to the desired porosity I can regulate it. Accordingly, the porosity of the positive electrode active material layer may be determined according to Equation 1 below.
  • sample volume is the thickness of the 25 cm 2 X cathode active material layer.
  • the porosity of the conductive layer is measured in the same manner using Equation 1, and then the conductivity is measured in the pore volume of the sample including the conductive layer.
  • the pore volume and porosity of the conductive layer can be obtained through Equation 2 below.
  • the conductive layer volume is the thickness of the 25 cm 2 X conductive layer.
  • Figure 1a is a schematic diagram showing a cross-sectional structure of the anode according to an embodiment of the present invention
  • Figure 1b is a plan view schematically showing the surface of the anode.
  • 1A and 1B are merely examples for describing the present invention and the present invention is not limited thereto.
  • a description will be given with reference to FIGS. 1A and 1B.
  • Secondary battery positive electrode 10 is a positive electrode current collector (1), a porous positive electrode active material layer (2) located on the surface of the positive electrode current collector and the positive electrode active material layer located on the surface
  • the conductive layer 3 is included.
  • the positive electrode current collector 1 is not particularly limited as long as it has conductivity without causing chemical change in the battery, for example, stainless steel, Aluminum, nickel, titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver, or the like on the surface of aluminum or stainless steel may be used.
  • the positive electrode current collector may have a thickness of about 3 to 500 ⁇ m, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive electrode active material.
  • it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.
  • the positive electrode active material layer 2 is located on at least one surface of the positive electrode current collector 1, the positive electrode active material 2a and The first carbon nanotube 2b is included as the conductive material.
  • the positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound), and specifically includes at least one metal such as cobalt, manganese, nickel or aluminum and lithium. It may include a lithium composite metal oxide.
  • the lithium composite metal oxide is a lithium-manganese oxide (eg, LiMnO 2 , LiMn 2 O 4 Etc.), lithium-cobalt oxides (e.g., LiCoO 2, etc.), lithium-nickel oxides (e.g., LiNiO 2, etc.), lithium-nickel-manganese oxides (e.g., LiNi 1 -Y 1 Mn Y1 O 2 (here, 0 ⁇ Y1 ⁇ 1), LiMn 2 - z1 Ni z1 O 4 ( here, 0 ⁇ Z1 ⁇ 2) and the like), lithium-nickel-cobalt-based oxide (for example, LiNi 1- Y2 Co Y2 O 2 (here, 0 ⁇ Y2 ⁇ 1), etc., lithium-manganese-cobalt-based oxides (eg, LiCo 1 - Y3 Mn Y3 O 2 (here, 0 ⁇ Y3 ⁇ 1), LiMn 2
  • LiCoO 2 , LiMnO 2 , LiNiO 2 , and lithium nickel manganese cobalt oxides may be improved in capacity and stability of the battery.
  • the metal elements except lithium is selected from the group consisting of W, Mo Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, and Nb. It may be doped by any one or more than two elements. As described above, when the metal element is further doped in the lithium composite metal oxide, the structural stability of the cathode active material may be improved, and as a result, the output characteristics of the battery may be improved. In this case, the content of the doping element included in the lithium composite metal oxide may be appropriately adjusted within a range that does not lower the characteristics of the positive electrode active material, specifically, may be 0.02 atomic% or less.
  • the lithium composite metal oxide may be to include a compound of formula (1).
  • M1 includes any one or two or more elements selected from the group consisting of Al and Mn
  • M2 is W, Mo Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba
  • It includes any one or two or more elements selected from the group consisting of Ca, and Nb, 1.0 ⁇ a ⁇ 1.5, 0 ⁇ x ⁇ 0.5, 0 ⁇ y ⁇ 0.5, 0 ⁇ z ⁇ 0.02, 0 ⁇ x + y ⁇ 0.7, more specifically, 1.0 ⁇ a ⁇ 1.2, 0 ⁇ x ⁇ 0.5, 0 ⁇ y ⁇ 0.5, 0.0005 ⁇ z ⁇ 0.02, 0 ⁇ x + y ⁇ 0.7)
  • the cathode active material may have an average particle diameter (D 50 ) of 3 to 20 ⁇ m in consideration of the specific surface area and the positive electrode mixture density. If the average particle diameter of the positive electrode active material is less than 3 ⁇ m, there is a fear of dispersibility in the positive electrode mixture due to aggregation between the positive electrode active materials, and if it exceeds 20 ⁇ m, the mechanical strength of the positive electrode active material and the specific surface area may be reduced. In addition, when considering the effect of improving the rate characteristics and initial capacity characteristics due to the specific structure may have an average particle diameter (D 50 ) of 3 to 15 ⁇ m. In the present invention, the average particle diameter (D 50 ) of the positive electrode active material may be defined as the particle diameter at 50% of the particle diameter distribution.
  • the average particle diameter (D 50 ) of the positive electrode active material can be measured using, for example, a laser diffraction method.
  • a laser diffraction method for example, the particles of the positive electrode active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000) and After irradiating an ultrasonic wave of 28 kHz with an output of 60 W, the average particle diameter (D 50 ) at a 50% reference of the particle diameter distribution in the measuring device can be calculated.
  • the positive electrode active material 2a may be included in an amount of 80 to 99 wt% based on the total weight of the positive electrode active material layer 2. If the content of the positive electrode active material is less than 80% by weight, the capacity characteristics of the battery may be deteriorated. If the content of the positive electrode active material is higher than 99% by weight, the contact probability of the positive electrode active material and the conductive material is lowered due to the decrease of the content of the conductive material, and thus the electrically inactive active material. There is a possibility that the output characteristics of the battery may decrease due to the increase of.
  • the first carbon nanotubes 2b are secondary structures formed by collecting a plurality of carbon nanotube units, and the plurality of carbon nanotube units are arranged side by side in substantially the same orientation in the longitudinal direction of the unit.
  • the bundle may have a bundle or rope shape, or may have an entangle shape in which the carbon nanotube units are entangled.
  • the first carbon nanotubes may be bundled.
  • the carbon nanotubes may have different physical properties depending on the crystallinity and structure and shape of the units constituting the carbon nanotubes, the structure and shape of the secondary particles composed of the units, and the content of metal elements included in the carbon nanotubes. Accordingly, by controlling any one or two or more of the above factors, it is possible to have the physical properties required according to the use of the carbon nanotubes. Specifically, the carbon nanotubes may exhibit low resistance as the crystallinity is high during growth, the defects are smaller, and the thickness of the walls forming the carbon nanotubes is thinner. In addition, the lower the resistance of the carbon nanotubes themselves, the lower the intra-electrode resistance when applied to electrode production, and as a result the battery performance can be improved.
  • the first carbon nanotubes used in the present invention may include any one or two or more of single-walled, double-walled, and multi-walled carbon nanotube units.
  • the first carbon nanotubes may have a diameter of 10 to 100 nm and a length of 3 to 10 ⁇ m. When the first carbon nanotube unit meets the above diameter and length conditions, it may be easy to form an electrically conductive network without fear of non-uniform dispersion in the positive electrode mixture.
  • the first carbon nanotubes may have a specific surface area of 20 to 2000 m 2 / g as secondary particles, together with the diameter and length conditions of the unit. If the specific surface area of the first carbon nanotube is less than 20 m 2 / g, the improvement may be insignificant due to the reduction of the reaction area, and if it exceeds 2000 m 2 / g, it may be difficult to form a conductive network. More specifically, considering the remarkable effect of the improvement according to the control of the specific surface area of the first carbon nanotubes, the specific surface area of the first carbon nanotubes may be 100 to 400m 2 / g.
  • the specific surface area of the carbon nanotubes is measured by the BET method, and specifically, it can be calculated from the nitrogen gas adsorption amount under the liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan. have.
  • the first carbon nanotube may have a bulk density of 0.01 to 200 kg / m 3 , more specifically 0.01 to 10 kg / m 3 , even more specifically 0.01 to 1 kg / m 3 .
  • Carbon nanotubes may exhibit excellent dispersibility as the bulk density is low, but when the bulk density is too low, the amount of carbon nanotube units in the electrode may be reduced, thereby lowering the electrical conductivity in the electrode.
  • the first carbon nanotubes used in the present invention may exhibit excellent electrical conductivity by having the bulk density in the above range.
  • the bulk density of the carbon nanotubes may be determined according to Equation 3 below.
  • Such first carbon nanotubes may be obtained commercially, or may be manufactured and used directly.
  • the method may be manufactured using a conventional method such as an arc discharge method, a laser evaporation method or a chemical vapor deposition method, and the aforementioned physical properties may be controlled by controlling the type of catalyst, heat treatment temperature, and impurity removal method in the manufacturing process. Can be implemented.
  • the first carbon nanotubes may be included in an amount of 0.2 to 2 wt% based on the total weight of the cathode active material layer. If the content of the first carbon nanotube is less than 0.2% by weight, there is a possibility that the output characteristics may decrease due to the decrease in conductivity and resistance in the anode. There is a fear that the output characteristics may decrease due to an increase in the Li transfer resistance in the electrolyte.
  • the cathode active material layer 2 may further include a heterogeneous conductive material (not shown) having a different shape such as particulate, fibrous or plate together with the first carbon nanotubes described above. It may further comprise 0.2 to 6% by weight based on the total weight of the active material layer.
  • a conductive material having a shape anisotropy is used as described above, it is easy to form a three-phase interface between the positive electrode active material and the electrolyte, thereby increasing the reactivity.
  • the pores between the positive electrode active materials can be maintained to provide excellent pore characteristics. You can have it.
  • the average particle diameter (D 50 ) may be 10 to 150 nm, and the specific surface area may be 20 to 600 m 2 / g.
  • D 50 average particle diameter
  • the reactivity can be improved by raising the electron supply property in the three-phase interface of a positive electrode active material and electrolyte.
  • the average particle diameter of the particulate conductive material is less than 10 nm or the specific surface area exceeds 170 m 2 / g, agglomeration of the particulate conductive materials greatly reduces the dispersibility in the positive electrode mixture, and the average particle diameter exceeds 45 nm or the ratio If the surface area is less than 40 m 2 / g, since the size is excessively large, in the conductive material arrangement according to the porosity of the positive electrode active material, it may be partially biased without being uniformly dispersed throughout the positive electrode mixture.
  • the average particle diameter of the particulate conductive material may be measured in the same manner as in the cathode active material.
  • the particulate conductive material may be used without particular limitation as long as it has conductivity and meets its morphological conditions.
  • the particulate conductive material may be a non-graphite carbon material in consideration of the excellent improvement effect of using the particulate conductive material.
  • the particulate conductive material may be carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or denka black, and any one or a mixture of two or more thereof may be used.
  • the plate-shaped conductive material is a conductive material having an aggregate structure in which two surfaces corresponding to each other are flat and the size in the horizontal direction is larger than the size in the vertical direction, and of course, the plate-like conductive material is similar to the plate shape. Flakes, scales, and the like, which are shaped, may also be included.
  • the plate-like conductive material having a size in the above range can easily form a conductive network in the positive electrode mixture when mixed with the above-mentioned particulate and fibrous conductive materials, and can maintain the pore characteristics well.
  • the plate-like conductive material may be a ratio of the diameter in the flat plane to the thickness of 10 to 200.
  • the "diameter" of a plate-shaped conductive material means the longest length of the line which connected the two points in the closed curve which the perimeter of a flat surface makes.
  • the "closed curve” means a curve in which a point on the curve moves in one direction and returns to the starting point.
  • the "thickness" of a plate-shaped electrically conductive material means the average length between two flat surfaces.
  • the cathode active material layer 2 may further include a binder (not shown) to improve adhesion between the cathode active material particles and adhesion between the cathode active material and the cathode current collector, as necessary.
  • the binder is specifically polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene Butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, and the like, and one or more of these may be used.
  • the binder may be included in an amount of 1 to 10% by weight based on the total weight of the positive electrode active material layer.
  • the positive electrode active material layer 2 having the above-described configuration exhibits porosity including a plurality of pores existing between the particles of the positive electrode active material 2a and between the positive electrode active material 2a and the first carbon nanotubes 2b.
  • the voids formed inside the positive electrode active material layer may be a passage for mass transfer of an electrolyte or the like to reduce the mass transfer resistance in the positive electrode active material layer.
  • the positive electrode active material layer 2 has a porosity of 10% by volume to 50% by volume, more specifically 20% by volume to 45% by volume, by controlling the properties and contents of the components constituting the positive electrode active material layer. It may have a porosity of.
  • the conductive layer 3 is located on the surface of the positive electrode active material layer 2, a plurality of second carbon nanotubes (3a) Intertwined three-dimensionally connected porous network structures (see FIGS. 1A and 1B).
  • the second carbon nanotubes 3a may be the same as the first carbon nanotubes included in the cathode active material layer, and may be the same as or different from the first carbon nanotubes.
  • the second carbon nanotubes may have a smaller diameter and a longer length than the first carbon nanotubes when considering functional differences according to positions in the anode.
  • Figure 2a is a schematic diagram showing a cross-sectional structure of the anode prepared using a conventional carbon nanotube
  • Figure 2b is a plan view schematically showing the surface of the anode.
  • FIG. 2A and FIG. 2B in the case of the conventional anode 100, since the carbon nanotubes 12b are distributed inside the cathode active material layer 12, at the contact portion with the cathode current collector 11, Although the conductivity can be maintained, the contact probability with the carbon nanotubes 12b is lowered toward the surface of the cathode active material layer 12, so that the electrically inactive cathode active material 12a is present.
  • Such battery inert positive electrode active material 12a causes a decrease in battery capacity.
  • the conductive layer when the conductive layer is further formed by applying the conductive layer slurry (not shown), it may not be easy to form a conductive layer having a thin thickness of 0.02 or less relative to the thickness ratio of the positive electrode active material.
  • the surface of the positive electrode active material is entirely covered with the conductive layer, Li ions in the electrolyte are not desired to move to the electrode, and the rate characteristic may be lowered.
  • the positive electrode 10 is a positive electrode active material is a conductive layer 3 including a porous network structure consisting of the second carbon nanotubes (3a)
  • the inert positive electrode active material is prevented from being generated through contact with the positive electrode active material 2a present on the surface of the positive electrode active material layer, and at the same time, By connecting to the one carbon nanotube (2b) to form an electrically conductive path, it is possible to reduce the electron transfer resistance in the positive electrode active material layer.
  • the conductive layer 3 including the porous network structure may be formed at a thickness ratio of at least 1: 001 to 1: 0.05 with respect to the thickness of the cathode active material layer 2. If the thickness of the conductive layer is less than 0.001 thickness ratio, the carbon nanotube network may not be sufficiently formed on the positive electrode active material layer, and if the thickness exceeds 0.05, pores in the formed carbon nanotube network may be blocked.
  • the thickness ratio of the conductive layer 3 to the cathode active material layer 2 is preferably 0.001 to 0.01: 1, and more specifically, may be formed in a thickness ratio of 0.001 to 0.005.
  • the positive electrode active material layer of the present invention is formed to a thickness of 1: 0.02 to 0.05 compared to the thickness, since the structure is formed as a network structure on the surface of the positive electrode active material layer, unlike the prior art, Li ions in the electrolyte move to the electrode To be desired, the rate characteristic can be improved over the prior art.
  • the second carbon nanotubes 3a included in the conductive layer 3 may be determined in consideration of the content of the total carbon nanotubes included in the final anode, and specifically, the content of the total carbon nanotubes in the anode It may be included so as not to exceed four times. If the total carbon nanotube content in the positive electrode exceeds 4 times, increasing the thickness of the conductive layer may interfere with the transfer of the electrolyte into the active material layer, thereby increasing resistance.
  • the first carbon nanotubes: the second carbon nanotubes may be included in a weight ratio of 1: 0.08 to 0.42.
  • the carbon nanotube network may not be sufficiently formed on the positive electrode active material layer, and if it exceeds 0.42, the pores inside the three-dimensional network structure formed by the second carbon nanotube The degree can be lowered and the mass transfer effect can be reduced.
  • the porous network structure of the second carbon nanotubes 3a includes pores between the second carbon nanotubes in the structure. This may control the size and porosity of the pores in the porous network structure by controlling the diameter and content of the second carbon nanotubes. 2) Porosity is higher than porosity. Thus, having a higher porosity can prevent an increase in mass transfer resistance.
  • the porosity of the conductive layer 3 may have + 10% or more more than the porosity in the positive electrode active material 2 layer. More specifically, the porosity of the conductive layer may have a porosity of 20% by volume to 60% by volume, and more specifically 30% by volume to 60% by volume.
  • the cathode active material layer has a porosity of 10 to 50% by volume based on the total volume of the cathode active material layer, and the thickness of the conductive layer is based on the total thickness of the cathode active material layer.
  • the porosity of the conductive layer may have a porosity of 10% by volume or more higher than the positive electrode active material layer.
  • the positive electrode active material layer has a porosity of 10 to 50% by volume with respect to the total volume of the positive electrode active material layer
  • the thickness of the conductive layer is a positive electrode active material layer 0.001 to 0.01: 1 based on the total thickness
  • the porosity of the conductive layer may be 20% by volume to 60% by volume or more.
  • a secondary battery positive electrode according to an embodiment of the present invention having a structure as described above,
  • step 1 Adding a second carbon nanotube to the dispersion medium to prepare a composition for forming a conductive layer on which a second carbon nanotube film is formed on the surface of the dispersion medium (step 1);
  • step 2 After impregnating the electrode assembly having a positive electrode active material layer including a positive electrode active material and a first carbon nanotube on at least one surface of the positive electrode current collector in the conductive layer forming composition, the second carbon nanotube film is formed on the surface of the positive electrode active material layer.
  • Lifting the electrode assembly to position to form a conductive layer can be manufactured by a manufacturing method comprising a.
  • a method of manufacturing the positive electrode for a secondary battery is provided.
  • FIG. 3 is a process diagram schematically showing a method of manufacturing a cathode for a secondary battery according to an embodiment of the present invention. 3 is only an example for describing the present invention and the present invention is not limited thereto. Hereinafter, each step will be described with reference to FIG. 3.
  • step 1 for manufacturing the secondary battery positive electrode is a step of preparing a composition for forming a conductive layer (S1).
  • the conductive layer forming composition may be prepared by adding carbon nanotubes to a dispersion medium.
  • the carbon nanotubes may not be mixed in the dispersion medium, and may be formed on the dispersion medium to form a three-dimensional porous network film on the surface of the dispersion medium.
  • 2 carbon nanotubes are added dropwise, and then the second carbon nanotubes are dispersed on a dispersion medium by ultrasonic dispersion.
  • the second carbon nanotubes may be the same as the first carbon nanotubes described above, and the amount of the second carbon nanotubes may be appropriately determined in consideration of the thickness of the conductive layer to be finally manufactured and the total content of the carbon nanotubes in the positive electrode active material.
  • Amide type polar organic solvent such as dimethylformamide (DMF), diethyl formamide, dimethyl acetamide (DMAc), N-methyl pyrrolidone (NMP); Methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl Alcohols such as 2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol; Glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; Polyhydric alcohols such as glycerin
  • a dispersion medium having an appropriate polarity difference may be selected in consideration of the spreadability in forming the carbon nanotube film, and more specifically, an alcohol solvent may be used.
  • step 2 is a step of forming a conductive layer on the cathode active material layer using the composition for forming a conductive layer prepared in step 1 (S2).
  • a cathode active material layer is formed on a cathode current collector to prepare a cathode assembly, and then impregnated in the composition for forming a conductive layer prepared in Step 1, so that the carbon nanotube film is positioned on the active material layer of the cathode assembly. This can be done by lifting slowly.
  • the positive electrode assembly is a positive electrode active material, carbon nanotubes and optionally a binder in a solvent to prepare a composition for forming a positive electrode active material layer, it is applied to at least one surface of the positive electrode current collector and dried, or the composition for forming the positive electrode active material layer Can be prepared by casting a film on a separate support and then laminating the film obtained by peeling from the support on a positive electrode current collector.
  • the type and content of the cathode assembly, the cathode active material, the carbon nanotubes and the binder are the same as described above.
  • the solvent may be a solvent generally used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or acetone. Water, and the like, one of these alone or a mixture of two or more thereof may be used.
  • the amount of the solvent may be sufficient to dissolve or disperse the electrode active material and the binder in consideration of the coating thickness of the composition and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity during application for electrode production.
  • the second carbon nanotube film located on the surface of the conductive layer forming composition is rolled up on the positive electrode active material layer.
  • a thin carbon nanotube film floating on the surface of the conductive layer forming composition may be formed on the cathode active material layer as it is.
  • the impregnation time may be approximately 10 seconds to 60 seconds, and if it exceeds 60 seconds, the binder in the positive electrode active material may be modified to cause a structural change.
  • the cathode active material layer may be gradually lifted at a speed of approximately 0.13 m / min to 0.16 m / min, specifically 0.15 m / min.
  • the method of the present invention for 5 to 7 hours at 5 to 20 pa, 60 °C to 90 °C temperature, specifically 10 pa, 80 °C temperature for 6 hours to evaporate the dispersion medium present in the carbon nanotube film During drying step S3 can optionally be carried out.
  • a conductive layer including a porous mesh structure of carbon nanotubes is positioned on the anode active material layer, and the carbon nanotubes in the conductive layer are connected to the carbon nanotubes in the anode active material layer.
  • the anode according to the exemplary embodiment of the present invention has a uniform and stable conductive network formed throughout the cathode active material layer, thereby greatly reducing the charge transfer resistance in the electrode and stably improving output characteristics.
  • the anode according to an embodiment of the present invention can prevent an increase in mass transfer resistance into the cathode active material layer through porosity control in the structure.
  • an electrochemical device including the anode is provided.
  • the electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.
  • the lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above.
  • the lithium secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.
  • the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.
  • the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery.
  • the negative electrode current collector may be formed on a surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used.
  • the negative electrode current collector may have a thickness of about 3 to 500 ⁇ m, and like the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material.
  • it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.
  • the negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.
  • the negative electrode active material layer is coated with a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material on a negative electrode current collector and dried, or casting the negative electrode forming composition on a separate support It may be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.
  • a compound capable of reversible intercalation and deintercalation of lithium may be used.
  • Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon;
  • Metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys;
  • Metal oxides capable of doping and undoping lithium such as SiO x (0 ⁇ x ⁇ 2), SnO 2 , vanadium oxide, lithium vanadium oxide;
  • a composite including the metallic compound and the carbonaceous material such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used.
  • a metal lithium thin film may be used as the anode active material.
  • the carbon material both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is typical.
  • the binder and the conductive material may be the same as described above in the positive electrode.
  • the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular to the ion movement of the electrolyte It is desirable to have a low resistance against the electrolyte and excellent electrolytic solution-moisture capability.
  • a porous polymer film for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used.
  • a porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and the like may be used.
  • a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.
  • examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.
  • the electrolyte may include an organic solvent and a lithium salt.
  • the organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move.
  • the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, ⁇ -butyrolactone or ⁇ -caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a
  • carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds (for example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable.
  • the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of about 1: 1 to about 1: 9, so that the performance of the electrolyte may be excellent.
  • the lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery.
  • the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAl0 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN (C 2 F 5 SO 3 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN (CF 3 SO 2 ) 2 .
  • LiCl, LiI, or LiB (C 2 O 4 ) 2 and the like can be used.
  • the concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.
  • the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, tri, etc. for the purpose of improving battery life characteristics, reducing battery capacity, and improving discharge capacity of the battery.
  • haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, tri, etc.
  • Ethyl phosphite triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imida
  • One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be included. In this case, the additive may be included in 0.1 to 5% by weight based on the total weight of the electrolyte.
  • the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate
  • portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicle fields such as hybrid electric vehicle (HEV).
  • HEV hybrid electric vehicle
  • a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.
  • the battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.
  • Power Tool Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.
  • the porosity of the positive electrode active material layer and the conductive layer in the following Examples and Comparative Examples were determined in accordance with the following equations (1) and (2), respectively, converted to volume based on the true density of each material, corresponding to the desired porosity
  • the thickness was adjusted by rolling the electrode.
  • sample volume is the thickness of the 25 cm 2 X cathode active material layer.
  • the conductive layer volume is the thickness of the 25 cm 2 X conductive layer.
  • second carbon nanotubes (unit length: 5 ⁇ m, diameter: 10 nm, specific surface area: 300 m 2 / g, bulk density: 0.13 kg / m 3 in bundle carbon nanotubes) were slowly added to the surface of 100 ml of isopropyl alcohol. After dropping, ultrasonic dispersion was performed for 10 minutes to prepare a composition for forming a conductive layer on which a film including a three-dimensional porous network structure composed of second carbon nanotubes was formed on the surface of isopropyl alcohol.
  • the electrode assembly After impregnating the prepared cathode assembly into the composition for forming a conductive layer for 30 seconds, the electrode assembly was gently lifted for 3 seconds at a rate of 0.15 m / min so that the second carbon nanotube film was positioned on the surface of the cathode active material layer.
  • Second carbon nanotubes (length of unit: 7 ⁇ m, diameter: 9 nm, specific surface area: 300 m 2 / g, bulk density: 0.13 kg / m 3) when preparing the composition for forming a conductive layer of Example 1 Nanotube) 0.9g was slowly added to the surface of 100ml isopropyl alcohol, and then ultrasonically dispersed for 10 minutes to form a conductive layer having a film including a three-dimensional porous network structure composed of second carbon nanotubes on the surface of isopropyl alcohol. A composition for preparation was prepared.
  • Second carbon nanotubes (length of the unit: 3 ⁇ m, diameter: 10 nm, specific surface area: 300 m 2 / g, bulk density: 0.13 kg / m 3) when manufacturing the composition for forming a conductive layer of Example 1 0.5g) is slowly added dropwise to 100ml surface of isopropyl alcohol, and then ultrasonically dispersed for 10 minutes to form a conductive layer having a film including a three-dimensional porous network structure composed of second carbon nanotubes on the surface of isopropyl alcohol.
  • Example 1 Except not forming a conductive layer on the surface of the positive electrode active material layer in Example 1 was prepared in the same manner as in Example 1 to prepare a positive electrode (see Table 1 below).
  • the carbon nanotube content is increased to a ratio of 0.056 relative to the positive electrode active material layer so that there is little difference between the porosity in the conductive layer and the porosity in the positive electrode active material layer.
  • Lithium secondary batteries were prepared using the positive electrodes prepared in Examples 1 to 4, Comparative Examples 1 to 4, and Reference Examples, respectively.
  • a negative electrode active material a natural graphite, a carbon black conductive material, an SBR binder, and carboxymethyl cellulose (CMC) are mixed in an N-methylpyrrolidone solvent in a weight ratio of 96: 1: 2: 1 to form a negative electrode.
  • CMC carboxymethyl cellulose
  • LiPF 6 lithium hexafluorophosphate
  • Coin cells using a negative electrode of Li metal prepared by using the respective anodes prepared in Examples 1 to 4, Comparative Examples 1 to 4, and Reference Examples were to have a constant current (CC) of 4.25V at 25 ° C.
  • the battery was charged until then, and then charged at a constant voltage (CV) of 4.25V to perform a first charge until the charging current became 0.05 mAh.
  • CV constant voltage
  • the battery was discharged to a constant current of 0.1C until 3.0V, and the discharge capacity of the first cycle was measured. Then, rate characteristics were evaluated by varying the discharge conditions at 2C. The results are shown in FIG. 6.
  • the anodes of Examples 1 to 4 are the anodes of Comparative Examples 1 and 4 that do not form a conductive layer, and Comparative Example 2, the conductive layer having a small difference in porosity in the conductive layer and a porosity in the cathode active material layer is less than 10% by volume.
  • the positive electrode of Comparative Example 3 in which excessive carbon nanotubes were included in an excessive amount, excellent rate characteristics were shown.
  • the positive electrode including the conductive layer of the reference example formed by applying the conductive layer slurry using the existing coating method it is difficult to control the thickness ratio of the conductive layer to the positive electrode active material layer to 1: 0.02 or less, and the positive electrode active material layer
  • the conductive layer By forming the conductive layer on the entire surface of the surface, lithium ions in the electrolyte were not smoothly moved to the electrode, and the rate characteristic was lowered compared to the anodes of Examples 1 to 4.
  • the positive electrode of Example 1 exhibited excellent rate characteristics compared to the positive electrode of Comparative Example 1 including a positive electrode active material layer having the same characteristics but not containing a conductive layer. From this, it can be seen that the rate characteristic can be improved by forming the conductive layer.
  • the positive electrode of Example 1 includes a positive electrode active material layer and a conductive layer, but Comparative Example 2 having a porosity difference between the conductive layer and the positive electrode active material layer is less than 10% by volume, and the conductive material of the conductive layer is too large to form a thick conductive layer.
  • Comparative Example 3 showed excellent rate characteristics. This is because the material resistance is increased due to the thickness or low porosity of the conductive layer.
  • the positive electrode of Example 2 exhibits excellent rate characteristics compared to the positive electrode of Comparative Example 4, which includes a positive electrode active material layer having the same characteristics but does not include a conductive layer, but has a slightly lower rate characteristic than the positive electrode of Example 1. Indicated. This is because in the case of Example 2, the content of the conductive material in the positive electrode active material layer is reduced compared to Example 1, so that the conductive network in the active material layer is not sufficiently formed.
  • the positive electrode of Examples 1 and 2 has a network-like conductive layer in which the positive electrode active material is partially exposed, compared with the positive electrode of the reference example including the conductive layer formed by applying the conductive layer slurry, the material transfer in the conductive layer is performed. High rate characteristics can be realized by suppressing the increase in resistance.
  • the lithium secondary batteries prepared in Examples 1 to 4 can significantly exhibit an excellent output as the interface resistance is greatly reduced compared to Comparative Examples 1 to 4.
  • a conductive layer including carbon nanotubes on the cathode active material layer to form an electrical network on the surface side it can significantly reduce the interface resistance.
  • the interfacial resistance was not the same level or significantly increased, it can be seen that the mass transfer resistance can be reduced by controlling the porosity of the conductive layer.

Abstract

The present invention provides a cathode for a secondary battery and a secondary battery comprising the same, wherein the cathode for a secondary battery comprises: a cathode current collector; a porous cathode active material layer positioned on the surface of the cathode current collector and comprising a cathode active material and a first carbon nanotube; and a conductive layer on which the cathode active material layer is positioned on the surface thereof, wherein the conductive layer comprises a porous network structure formed by a plurality of second carbon nanotubes and the porosity of the cathode active material layer is a porosity of +10 volume% or more. The cathode for a secondary battery according to the present invention forms an electrical network inside and across the surface of the cathode active material layer by using carbon nanotubes having strength properties as well as excellent electrical conductivity, such that it is possible to keep material resistance in the active material layer low while greatly reducing charge transfer resistance whereby the output properties of the battery can be remarkably improved.

Description

이차전지용 양극 및 이를 포함하는 이차전지Anode for Secondary Battery and Secondary Battery Having Same
관련 출원(들)과의 상호 인용Cross Citation with Related Application (s)
본 출원은 2015년 11월 30일자 한국 특허 출원 제10-2015-0169150호 및 2016년 11월 30일자 한국 특허 출원 제10-2016-0161525호에 기초한 우선권의 이익을 주장하며, 해당 한국 특허 출원의 문헌에 개시된 모든 내용은 본 명세서의 일부로서 포함된다.This application claims the benefit of priority based on Korean Patent Application No. 10-2015-0169150 dated November 30, 2015 and Korean Patent Application No. 10-2016-0161525 dated November 30, 2016. All content disclosed in the literature is included as part of this specification.
기술분야Technical Field
본 발명은 양극 전체에 걸친 전기적 네트워크의 형성으로 전하 전달 저항이 감소되어 전지의 출력 특성을 개선시킬 수 있는 이차전지용 양극 및 이를 포함하는 이차전지에 관한 것이다. The present invention relates to a secondary battery positive electrode and a secondary battery including the same, which can improve the output characteristics of the battery by reducing the charge transfer resistance by the formation of an electrical network across the positive electrode.
모바일 기기에 대한 기술 개발과 수요가 증가함에 따라 에너지원으로서 이차전지의 수요가 급격히 증가하고 있다. 이러한 이차전지 중 높은 에너지 밀도와 전압을 가지며, 사이클 수명이 길고, 자기방전율이 낮은 리튬 이차전지가 상용화되어 널리 사용되고 있다. As technology development and demand for mobile devices increase, the demand for secondary batteries as a source of energy is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used.
리튬 이차전지는 리튬 이온의 흡장 방출이 가능한 양극 활물질을 포함하고 있는 양극과, 리튬 이온의 흡장 방출이 가능한 음극 활물질을 포함하고 있는 음극 사이에 미세 다공성 세퍼레이터가 개재된 전극 조립체에 리튬 이온을 함유한 비수 전해질을 포함한다. 또, 리튬 이차전지의 음극 활물질로는 리튬 금속, 리튬 금속과의 합금, 탄소계 물질 등 그 자체로 전도성을 갖는 물질이 사용되고 있으며, 양극 활물질로는, 리튬 코발트 산화물(LiCoO2), 리튬 망간 산화물(LiMn2O4) 또는 리튬 니켈 산화물(LiNiO2) 등의 전이금속 산화물, 이들 전이금속의 일부가 다른 전이금속으로 치환된 복합 산화물 등이 주로 사용되고 있다. The lithium secondary battery includes lithium ions in an electrode assembly having a microporous separator interposed between a positive electrode including a positive electrode active material capable of occluding and releasing lithium ions and a negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions. Nonaqueous electrolyte. In addition, as a negative electrode active material of a lithium secondary battery, a material having conductivity by itself, such as a lithium metal, an alloy with a lithium metal, a carbon-based material, and the like is used. As the positive electrode active material, lithium cobalt oxide (LiCoO 2 ) and lithium manganese oxide are used. Transition metal oxides such as (LiMn 2 O 4 ) or lithium nickel oxide (LiNiO 2 ), and composite oxides in which some of these transition metals are substituted with other transition metals are mainly used.
이와 같이 양극 활물질의 경우 그 자체의 전기 전도성이 낮기 때문에, 양극 제조시 전기 전도성이 높은 도전재가 반드시 포함되어야 한다.As described above, since the cathode active material has low electrical conductivity, a conductive material having high electrical conductivity must be included in the production of the cathode.
리튬 이차전지에 있어서, 양극은 양극활물질, 도전재, 및 선택적으로 바인더 등을 분산제로서의 용매와 일괄적으로 혼합하여 제조한 양극활물질 조성물을 양극 집전체에 도포 후 건조하여 제조된다. In a lithium secondary battery, a positive electrode is prepared by applying a positive electrode active material composition prepared by mixing a positive electrode active material, a conductive material, and optionally a binder and the like as a dispersant in a batch to a positive electrode current collector and then drying.
그러나 통상 양극활물질, 도전재 등은 분말상으로 사용되기 때문에 용매에 일괄적으로 투입하여 혼합할 경우, 용매와의 혼화성이 낮아 양극활물질 조성물 내 불균일하게 분산되게 된다. 그리고 이와 같이 양극활물질 및 도전재 등이 구성성분이 불균일하게 분산된 양극활물질 조성물을 양극 집전체에 도포하여 양극활물질층을 형성할 경우, 양극 집전체에 대한 균일 도포가 어렵고, 또 그 결과로 두께 균일성이 낮거나, 표면 결함을 갖는 양극활물질층이 형성되어 전지 성능 및 수명 특성을 저하시키게 된다.However, since the positive electrode active material, the conductive material, and the like are usually used in powder form, when mixed and mixed in a solvent, the compatibility with the solvent is low, so that the positive electrode active material and the conductive material are dispersed unevenly in the positive electrode active material composition. When the positive electrode active material composition in which the positive electrode active material and the conductive material are uniformly dispersed in the positive electrode current collector is formed on the positive electrode current collector, it is difficult to uniformly apply the positive electrode current collector to the positive electrode current collector. A cathode active material layer having low uniformity or surface defects is formed, thereby degrading battery performance and lifespan characteristics.
또, 도전재의 경우 수십 nm 수준의 미립자로 사용되기 때문에, 응집력이 강하여, 용매에 분산시 도전재 미립자 간의 응집이 일어나기 쉽다. 이로 인해 조성물내 도전재의 불균일한 분산이 발생하게 되면 양극활물질층 내 도전성 개선 효과가 불충분하여 전지의 출력 특성을 저하시키는 문제가 있다. In addition, since the conductive material is used as fine particles of several tens of nm level, the cohesive force is strong, and aggregation between the conductive material fine particles is likely to occur when dispersed in a solvent. As a result, when non-uniform dispersion of the conductive material in the composition occurs, the effect of improving the conductivity in the positive electrode active material layer is insufficient, thereby lowering the output characteristics of the battery.
또, 도전재를 사용하여 전극을 제작하는 경우 양극 합재 내 고형분의 함량이 도전재를 사용하지 않는 경우에 비해 높기 때문에, 전극 내 바인더의 마이그레이션(migration)이 발생하는 문제가 있다. 이 같은 바인더의 마이그레이션으로 인해 양극 제조시 양극활물질층의 양극 집전체에 대한 접착 강도에 불균일이 발생하게 되고, 그 결과로 양극활물질층이 양극 집전체로부터 분리되어 박리되어 버리는 문제가 있다. 이 경우 전지의 성능 자체를 현저하게 저하시킬 뿐만 아니라, 전지의 수명특성을 단축시키는 원인이 된다.In addition, when the electrode is manufactured using the conductive material, since the content of solids in the positive electrode mixture is higher than when the conductive material is not used, migration of the binder in the electrode occurs. Due to the migration of the binder, a nonuniformity occurs in the adhesive strength of the positive electrode active material layer to the positive electrode current collector during the production of the positive electrode, and as a result, the positive electrode active material layer is separated from the positive electrode current collector and peeled off. In this case, not only the performance of the battery itself is significantly lowered, but also the shortening of the battery life characteristics.
최근 고출력 이차전지에 대한 수요의 증가에 따라, 전지의 출력 특성을 높이기 위하여 전극내 전기전도성을 유지 또는 개선하면서도 동시에 도전재의 함량을 낮추어 전지의 에너지 밀도를 증가시키는 방법에 대한 연구가 이루어지고 있다. 그러나 단순히 도전재의 함량을 감소시키는 방법은 양극 표면에 존재하는 양극활물질과 도전재의 접촉 확률을 크게 감소시킴으로써 오히려 출력특성을 저하시키는 문제가 있다.In recent years, as the demand for high-output secondary batteries increases, research has been made on a method of increasing the energy density of batteries by maintaining or improving the electrical conductivity in the electrodes to increase the output characteristics of the batteries and at the same time lowering the content of the conductive material. However, the method of simply reducing the content of the conductive material has a problem of lowering the output characteristics by greatly reducing the contact probability of the positive electrode active material and the conductive material present on the surface of the positive electrode.
선행기술문헌Prior art literature
한국특허공개 제2005-0052266호Korean Patent Publication No. 2005-0052266
본 발명이 해결하고자 하는 제1 기술적 과제는, 양극 전체에 걸친 전기적 네트워크에 의해 전하 전달 저항이 감소되고, 또한 양극내 기공도 제어를 통한 물질 저항의 감소로 전지의 출력 특성이 개선된 이차전지용 양극을 제공하는 것을 목적으로 한다.The first technical problem to be solved by the present invention is a positive electrode for a secondary battery, the charge transfer resistance is reduced by the electrical network across the positive electrode, and the output characteristics of the battery is improved by reducing the material resistance through porosity control in the positive electrode The purpose is to provide.
또한, 본 발명이 해결하고자 하는 제2 기술적 과제는 상기 이차전지용 양극의 제조방법을 제공하는 것을 목적으로 한다.In addition, a second technical problem to be solved by the present invention is to provide a method for manufacturing the secondary battery positive electrode.
또한, 본 발명의 제3 기술적 과제는, 상기 이차전지용 양극을 포함하는 리튬 이차전지, 전지모듈 및 전지팩을 제공하는 것을 목적으로 한다.In addition, another object of the present invention is to provide a lithium secondary battery, a battery module and a battery pack including the secondary battery positive electrode.
상기 과제를 해결하기 위하여 본 발명의 일 실시예에 따르면, According to an embodiment of the present invention to solve the above problems,
양극 집전체, Anode current collector,
상기 양극 집전체의 표면 상에 위치하며, 양극활물질 및 제1 탄소 나노튜브를 포함하는 다공성 양극활물질층, 및Located on the surface of the positive electrode current collector, a porous positive electrode active material layer comprising a positive electrode active material and a first carbon nanotube, and
상기 양극활물질층이 표면 상에 위치하는 도전층을 포함하고,The cathode active material layer comprises a conductive layer located on the surface,
상기 도전층은 복수 개의 제2 탄소 나노튜브에 의해 형성된 다공성 망상 구조체를 포함하며, 양극활물질층의 기공도 + 10 부피% 이상의 기공도를 갖는 것인 이차전지용 양극이 제공된다.The conductive layer includes a porous network structure formed by a plurality of second carbon nanotubes, and has a porosity of a positive electrode active material layer + porosity of 10% by volume or more.
구체적으로, 상기 다공성 양극활물질층의 기공도(porosity)는 10 부피% 내지 50 부피%이며, 상기 도전층의 기공도는 20 부피% 내지 60 부피%의 기공도를 가질 수 있다.Specifically, the porosity of the porous cathode active material layer is 10% by volume to 50% by volume, and the porosity of the conductive layer may have a porosity of 20% by volume to 60% by volume.
본 발명의 다른 일 실시예에 따르면, According to another embodiment of the present invention,
제2 탄소 나노튜브를 분산매 중에 첨가하여 분산매의 표면 상에 제2 탄소 나노튜브 막이 형성된 도전층 형성용 조성물을 준비하는 단계; 및Adding a second carbon nanotube to the dispersion medium to prepare a composition for forming a conductive layer on which a second carbon nanotube film is formed on the surface of the dispersion medium; And
양극 집전체의 적어도 일면에, 양극활물질 및 제1 탄소 나노튜브를 포함하는 양극활물질층이 형성된 전극 조립체를 상기 도전층 형성용 조성물에 함침한 후, 상기 제2 탄소 나노튜브 막이 양극활물질층 표면 상에 위치하도록 전극 조립체를 들어올려 도전층을 형성하는 단계;를 포함하는 상기한 이차전지용 양극의 제조방법이 제공된다. After impregnating the electrode assembly having a cathode active material layer including a cathode active material and a first carbon nanotube on at least one surface of the cathode current collector in the composition for forming a conductive layer, the second carbon nanotube film is formed on the surface of the cathode active material layer. Lifting an electrode assembly to form a conductive layer to be located there is provided a method of manufacturing a positive electrode for a secondary battery comprising a.
본 발명의 또 다른 일 실시예에 따르면, 상기한 양극을 포함하는 리튬 이차전지, 전지모듈 및 전지팩이 제공된다.According to another embodiment of the present invention, a lithium secondary battery, a battery module, and a battery pack including the positive electrode are provided.
기타 본 발명의 실시예들의 구체적인 사항은 이하의 상세한 설명에 포함되어 있다.Other specific details of the embodiments of the present invention are included in the following detailed description.
본 발명에 따른 이차전지용 양극은, 우수한 전기전도성과 함께 강도 특성을 갖는 탄소 나노튜브를 이용하여 양극활물질층의 내부 및 표면에 걸쳐 전기적 네트워크를 형성함으로써, 활물질층내 물질 저항을 낮게 유지하면서도 전하 전달 저항을 크게 감소시킬 수 있으며, 그 결과 전지의 출력 특성을 현저히 개선시킬 수 있다.The secondary battery positive electrode according to the present invention forms an electrical network over the inside and the surface of the positive electrode active material layer using carbon nanotubes having strength characteristics along with excellent electrical conductivity, thereby maintaining a low material resistance in the active material layer while maintaining a charge transfer resistance. Can be greatly reduced, and as a result, the output characteristics of the battery can be significantly improved.
본 명세서에 첨부되는 다음의 도면들은 본 발명의 바람직한 실시예를 예시하는 것이며, 전술한 발명의 내용과 함께 본 발명의 기술사상을 더욱 이해시키는 역할을 하는 것이므로, 본 발명은 그러한 도면에 기재된 사항에만 한정되어 해석되어서는 아니 된다.The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.
도 1a은 본 발명의 일 실시예에 따른 양극의 단면 구조를 개략적으로 나타낸 모식도이다.1A is a schematic diagram schematically showing a cross-sectional structure of a positive electrode according to an embodiment of the present invention.
도 1b는 상기 양극 표면을 개략적으로 나타낸 평면도이다.1B is a plan view schematically illustrating the anode surface.
도 2a은 종래 섬유상의 도전재를 이용하여 제조한 양극의 단면 구조를 개략적으로 나타낸 모식도이다.2A is a schematic diagram schematically showing the cross-sectional structure of a positive electrode manufactured using a conventional fibrous conductive material.
도 2b는 종래 양극 표면을 개략적으로 나타낸 평면도이다.Figure 2b is a plan view schematically showing a conventional anode surface.
도 3은 본 발명의 일 실시예에 따른 양극의 제조 공정을 개략적으로 나타낸 순서도이다. 3 is a flow chart schematically showing a manufacturing process of a positive electrode according to an embodiment of the present invention.
도 4는 본 발명의 일 실시예에 따른 양극 표면에 대한 전자현미경(SEM) 사진이다. Figure 4 is an electron microscope (SEM) picture of the surface of the anode according to an embodiment of the present invention.
도 5는 종래 도전재층이 코팅된 양극 표면에 대한 전자현미경(SEM) 사진이다.Figure 5 is an electron microscope (SEM) picture of the surface of the anode coated with a conventional conductive material layer.
도 6은 실시예 1 내지 4, 비교예 1 내지 4, 및 참고예의 리튬 이차전지에 대한 율 특성 평가 결과를 나타낸 그래프이다.6 is a graph showing evaluation results of rate characteristics of lithium secondary batteries of Examples 1 to 4, Comparative Examples 1 to 4, and Reference Examples.
도 7은 실시예 1 내지 4, 비교예 1 내지 4, 및 참고예의 리튬 이차전지에 대한 저항 특성을 측정한 결과를 나타낸 그래프이다.7 is a graph illustrating results of measuring resistance characteristics of lithium secondary batteries of Examples 1 to 4, Comparative Examples 1 to 4, and Reference Examples.
도면 부호의 설명Explanation of Reference Numbers
1, 11: 양극 집전체1, 11: anode collector
2, 12: 양극활물질층2, 12: anode active material layer
2a, 12a: 양극활물질2a, 12a: positive electrode active material
2b: 제1 탄소 나노튜브2b: first carbon nanotube
12b: 탄소나노튜브12b: carbon nanotubes
3: 도전층3: conductive layer
3a: 제2 탄소 나노튜브3a: second carbon nanotubes
10, 100: 양극10, 100: anode
이하, 본 발명에 대한 이해를 돕기 위하여 본 발명을 더욱 상세하게 설명한다.Hereinafter, the present invention will be described in more detail to aid in understanding the present invention.
본 명세서 및 청구범위에 사용된 용어나 단어는 통상적이거나 사전적인 의미로 한정해서 해석되어서는 아니되며, 발명자는 그 자신의 발명을 가장 최선의 방법으로 설명하기 위해 용어의 개념을 적절하게 정의할 수 있다는 원칙에 입각하여 본 발명의 기술적 사상에 부합하는 의미와 개념으로 해석되어야만 한다.The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.
본 발명의 일 실시예에 따른 이차전지용 양극은, A secondary battery positive electrode according to an embodiment of the present invention,
양극 집전체,Anode current collector,
상기 양극 집전체의 표면 상에 위치하며, 양극활물질 및 제1 탄소나노튜브를 포함하는 다공성 양극활물질층, 및Located on the surface of the positive electrode current collector, a porous positive electrode active material layer comprising a positive electrode active material and a first carbon nanotube, and
상기 양극활물질층이 표면 상에 위치하는 도전층을 포함하고,The cathode active material layer comprises a conductive layer located on the surface,
상기 도전층은 복수 개의 제2 탄소나노튜브에 의해 형성된 다공성 망상 구조체를 포함하며, 양극활물질층의 기공도 + 10 부피% 이상의 기공도를 갖는 것인 이차전지용 양극이 제공된다.The conductive layer includes a porous network structure formed by a plurality of second carbon nanotubes, and has a porosity of a positive electrode active material layer + a porosity of 10% by volume or more.
구체적으로, 상기 다공성 양극활물질층의 기공도(porosity)는 10 부피% 내지 50 부피%이며, 상기 도전층의 기공도는 20 부피% 내지 60 부피%의 기공도를 가질 수 있다.Specifically, the porosity of the porous cathode active material layer is 10% by volume to 50% by volume, and the porosity of the conductive layer may have a porosity of 20% by volume to 60% by volume.
이와 같이, 본 발명의 일 실시예에 따른 이차전지용 양극은 양극활물질층의 내부 및 표면에 걸쳐 제1 및 제2 탄소나노튜브에 의한 전기적 네트워크를 형성함으로써, 활물질층내 전하 전달 저항을 크게 감소시킬 수 있으며, 더 나아가 양극활물질층내 기공과 도전층내 기공도 제어를 통해 양극활물질층 내부로의 물질 저항 증가를 억제할 수 있다. 그 결과, 전지의 출력 특성을 크게 향상시킬 수 있다.As such, the secondary battery positive electrode according to the embodiment of the present invention forms an electrical network by the first and second carbon nanotubes on the inside and the surface of the positive electrode active material layer, thereby greatly reducing the charge transfer resistance in the active material layer. In addition, it is possible to suppress the increase in material resistance into the positive electrode active material layer by controlling the porosity in the positive electrode active material layer and the porosity in the conductive layer. As a result, the output characteristics of the battery can be greatly improved.
본 발명에 있어서, 양극활물질층 및 도전층에서의 기공도는 pycnometer를 이용하여 측정된 25cm2 면적의 샘플의 진밀도를 기준으로 부피로 환산하고, 원하는 기공도에 해당하는 두께로 전극을 압연하여 조절할 수 있다. 이에 따라 일례로 양극활물질층의 기공도는 하기 수학식 1에 따라 결정될 수 있다. In the present invention, the porosity in the positive electrode active material layer and the conductive layer is converted into volume based on the true density of the sample of 25 cm 2 area measured using a pycnometer, and by rolling the electrode to a thickness corresponding to the desired porosity I can regulate it. Accordingly, the porosity of the positive electrode active material layer may be determined according to Equation 1 below.
[수학식 1][Equation 1]
Figure PCTKR2016014002-appb-I000001
Figure PCTKR2016014002-appb-I000001
상기 식에서, 샘플 부피는 25cm2 X 양극활물질층의 두께이다.Wherein the sample volume is the thickness of the 25 cm 2 X cathode active material layer.
이에 따라 도전층의 기공도의 경우, 상기 수학식 1을 이용하여 동일한 방식으로 도전층이 없는 샘플과 도전층이 포함된 샘플의 기공도를 측정한 다음 도전층이 포함된 샘플의 기공 부피에서 도전층이 없는 샘플의 기공 부피 차이를 계산한 다음, 하기 수학식 2를 통해 도전층의 기공 부피와 기공도를 구할 수 있다.Accordingly, in the case of the porosity of the conductive layer, the porosity of the sample without the conductive layer and the sample including the conductive layer is measured in the same manner using Equation 1, and then the conductivity is measured in the pore volume of the sample including the conductive layer. After calculating the pore volume difference of the layerless sample, the pore volume and porosity of the conductive layer can be obtained through Equation 2 below.
[수학식 2][Equation 2]
Figure PCTKR2016014002-appb-I000002
Figure PCTKR2016014002-appb-I000002
상기 식에서, 도전층 부피는 25cm2 X 도전층의 두께이다.Wherein the conductive layer volume is the thickness of the 25 cm 2 X conductive layer.
도 1a는 본 발명의 일 실시예에 따른 양극의 단면 구조를 개략적으로 나타낸 모식도이고, 도 1b는 상기 양극 표면을 개략적으로 나타낸 평면도이다. 도 1a 및 도 1b는 본 발명을 설명하기 위한 일 예일뿐 본 발명이 이에 한정되는 것은 아니다. 이하 도 1a 및 도 1b를 참고하여 설명한다.Figure 1a is a schematic diagram showing a cross-sectional structure of the anode according to an embodiment of the present invention, Figure 1b is a plan view schematically showing the surface of the anode. 1A and 1B are merely examples for describing the present invention and the present invention is not limited thereto. Hereinafter, a description will be given with reference to FIGS. 1A and 1B.
본 발명의 일 실시예에 따른 이차전지용 양극(10)은 양극 집전체(1), 상기 양극 집전체의 표면 상에 위치하는 다공성 양극활물질층(2) 및 상기 양극활물질층의 표면 상에 위치하는 도전층(3)을 포함한다.Secondary battery positive electrode 10 according to an embodiment of the present invention is a positive electrode current collector (1), a porous positive electrode active material layer (2) located on the surface of the positive electrode current collector and the positive electrode active material layer located on the surface The conductive layer 3 is included.
본 발명의 일 실시예에 따른 상기 이차전지용 양극(10)에 있어서, 양극 집전체(1)는 전지에 화학적 변화를 유발하지 않으면서 도전성을 가진 것이라면 특별히 제한되는 것은 아니며, 예를 들어 스테인리스 스틸, 알루미늄, 니켈, 티탄, 소성 탄소 또는 알루미늄이나 스테인레스 스틸 표면에 탄소, 니켈, 티탄, 또는 은 등으로 표면 처리한 것 등이 사용될 수 있다. 또, 상기 양극 집전체는 통상적으로 3 내지 500㎛의 두께를 가질 수 있으며, 상기 집전체 표면 상에 미세한 요철을 형성하여 양극활물질의 접착력을 높일 수도 있다. 예를 들어 필름, 시트, 호일, 네트, 다공질체, 발포체, 부직포체 등 다양한 형태로 사용될 수 있다.In the secondary battery positive electrode 10 according to an embodiment of the present invention, the positive electrode current collector 1 is not particularly limited as long as it has conductivity without causing chemical change in the battery, for example, stainless steel, Aluminum, nickel, titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver, or the like on the surface of aluminum or stainless steel may be used. In addition, the positive electrode current collector may have a thickness of about 3 to 500 μm, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.
또, 본 발명의 일 실시예에 따른 상기 이차전지용 양극(10)에 있어서, 양극활물질층(2)은 상기한 양극 집전체(1)의 적어도 일 표면 상에 위치하며, 양극활물질(2a) 및 도전재로서 제1 탄소나노튜브(2b)를 포함한다.In addition, in the secondary battery positive electrode 10 according to an embodiment of the present invention, the positive electrode active material layer 2 is located on at least one surface of the positive electrode current collector 1, the positive electrode active material 2a and The first carbon nanotube 2b is included as the conductive material.
상기 양극활물질은 리튬의 가역적인 인터칼레이션 및 디인터칼레이션이 가능한 화합물(리티에이티드 인터칼레이션 화합물)로서, 구체적으로는 코발트, 망간, 니켈 또는 알루미늄과 같은 1종 이상의 금속과 리튬을 포함하는 리튬 복합금속 산화물을 포함할 수 있다.The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound), and specifically includes at least one metal such as cobalt, manganese, nickel or aluminum and lithium. It may include a lithium composite metal oxide.
보다 구체적으로, 상기 리튬 복합금속 산화물은 리튬-망간계 산화물(예를 들면, LiMnO2, LiMn2O4 등), 리튬-코발트계 산화물(예를 들면, LiCoO2 등), 리튬-니켈계 산화물(예를 들면, LiNiO2 등), 리튬-니켈-망간계 산화물(예를 들면, LiNi1 -Y1MnY1O2(여기에서, 0<Y1<1), LiMn2 - z1Niz1O4(여기에서, 0＜Z1＜2) 등), 리튬-니켈-코발트계 산화물(예를 들면, LiNi1 - Y2CoY2O2(여기에서, 0<Y2<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo1 - Y3MnY3O2(여기에서, 0<Y3<1), LiMn2 - z2Coz2O4(여기에서, 0＜Z2＜2) 등), 리튬-니켈-망간-코발트계 산화물(예를 들면, Li(NipCoqMnr1)O2(여기에서, 0＜p＜1, 0＜q＜1, 0＜r1＜1, p+q+r1=1) 또는 Li(Nip1Coq1Mnr2)O4(여기에서, 0＜p1＜2, 0＜q1＜2, 0＜r2＜2, p1+q1+r2=2) 등), 또는 리튬-니켈-코발트-전이금속(M) 산화물(예를 들면, Li(Nip2Coq2Mnr3MS2)O2(여기에서, M은 Al, Fe, V, Cr, Ti, Ta, Mg 및 Mo로 이루어지는 군으로부터 선택되고, p2, q2, r3 및 s2는 각각 독립적인 원소들의 원자분율로서, 0＜p2＜1, 0＜q2＜1, 0＜r3＜1, 0＜s2＜1, p2+q2+r3+s2=1이다) 등) 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 화합물이 포함될 수 있다. 이중에서도 전지의 용량 특성 및 안정성을 높일 수 있다는 점에서 상기 리튬 복합금속 산화물은 LiCoO2, LiMnO2, LiNiO2, 리튬 니켈망간코발트 산화물(예를 들면, Li(Ni0.6Mn0.2Co0.2)O2, Li(Ni0.5Mn0.3Co0.2)O2, Li(Ni0.7Mn0.15Co0.15)O2 또는 Li(Ni0.8Mn0.1Co0.1)O2 등), 또는 리튬 니켈코발트알루미늄 산화물(예를 들면, Li(Ni0.8Co0.15Al0.05)O2) 등일 수 있으며, 리튬 복합금속 산화물을 형성하는 구성원소의 종류 및 함량비 제어에 따른 개선 효과의 현저함을 고려할 때 상기 리튬 복합금속 산화물은 Li(Ni0.6Mn0.2Co0.2)O2, Li(Ni0.5Mn0.3Co0.2)O2, Li(Ni0.7Mn0.15Co0.15)O2 또는 Li(Ni0.8Mn0.1Co0.1)O2 등일 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다.More specifically, the lithium composite metal oxide is a lithium-manganese oxide (eg, LiMnO 2 , LiMn 2 O 4 Etc.), lithium-cobalt oxides (e.g., LiCoO 2, etc.), lithium-nickel oxides (e.g., LiNiO 2, etc.), lithium-nickel-manganese oxides (e.g., LiNi 1 -Y 1 Mn Y1 O 2 (here, 0 <Y1 <1), LiMn 2 - z1 Ni z1 O 4 ( here, 0 <Z1 <2) and the like), lithium-nickel-cobalt-based oxide (for example, LiNi 1- Y2 Co Y2 O 2 (here, 0 <Y2 <1), etc., lithium-manganese-cobalt-based oxides (eg, LiCo 1 - Y3 Mn Y3 O 2 (here, 0 <Y3 <1), LiMn 2 - z2 Co z2 O 4 (here, 0 <Z2 <2) and the like, lithium-nickel-manganese-cobalt-based oxides (eg, Li (Ni p Co q Mn r1 ) O 2 (here, 0 <P <1, 0 <q <1, 0 <r1 <1, p + q + r1 = 1) or Li (Ni p1 Co q1 Mn r2 ) O 4 (where 0 <p1 <2, 0 <q1 <2, 0 <r2 <2, p1 + q1 + r2 = 2) or the like, or a lithium-nickel-cobalt-transition metal (M) oxide (for example, Li (Ni p2 Co q2 Mn r3 M S2 ) O 2 (here, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, p2, q2, r3 and s2 are each As an atomic fraction of independent elements, 0 <p2 <1, 0 <q2 <1, 0 <r3 <1, 0 <s2 <1, p2 + q2 + r3 + s2 = 1, etc.), etc.) Any one or two or more of these may be included. Among the lithium composite metal oxides, LiCoO 2 , LiMnO 2 , LiNiO 2 , and lithium nickel manganese cobalt oxides (eg, Li (Ni 0.6 Mn 0.2 Co 0.2 ) O 2 may be improved in capacity and stability of the battery. , Li (Ni 0.5 Mn 0.3 Co 0.2 ) O 2 , Li (Ni 0.7 Mn 0.15 Co 0.15 ) O 2 or Li (Ni 0.8 Mn 0.1 Co 0.1 ) O 2, etc.), or lithium nickel cobalt aluminum oxide (eg, Li (Ni 0.8 Co 0.15 Al 0.05 ) O 2 ), and the lithium composite metal oxide is Li (Ni 0.6 ) in consideration of the remarkable improvement effect of the type and content ratio of the member forming the lithium composite metal oxide. Mn 0.2 Co 0.2 ) O 2 , Li (Ni 0.5 Mn 0.3 Co 0.2 ) O 2 , Li (Ni 0.7 Mn 0.15 Co 0.15 ) O 2, or Li (Ni 0.8 Mn 0.1 Co 0.1 ) O 2 , and the like, and any one or a mixture of two or more thereof may be used. have.
또, 상기 리튬 복합금속 산화물에 있어서 리튬을 제외한 금속원소들 중 적어도 하나는 W, Mo Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, 및 Nb로 이루어지는 군으로부터 선택되는 어느 하나 또는 둘 이상의 원소에 의해 도핑될 수도 있다. 이와 같이 리튬 복합금속 산화물에 상기한 금속원소가 더 도핑될 경우, 양극활물질의 구조안정성이 개선되고, 그 결과 전지의 출력 특성이 향상될 수 있다. 이때, 리튬 복합금속 산화물 내 포함되는 도핑 원소의 함량은 양극활물질의 특성을 저하시키지 않는 범위내에서 적절히 조절될 수 있으며, 구체적으로는 0.02 원자% 이하일 수 있다. In the lithium composite metal oxide, at least one of the metal elements except lithium is selected from the group consisting of W, Mo Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, and Nb. It may be doped by any one or more than two elements. As described above, when the metal element is further doped in the lithium composite metal oxide, the structural stability of the cathode active material may be improved, and as a result, the output characteristics of the battery may be improved. In this case, the content of the doping element included in the lithium composite metal oxide may be appropriately adjusted within a range that does not lower the characteristics of the positive electrode active material, specifically, may be 0.02 atomic% or less.
보다 구체적으로, 본 발명의 일 실시예에 따른 양극활물질에 있어서, 상기 리튬 복합금속 산화물은 하기 화학식 1의 화합물을 포함하는 것일 수 있다.More specifically, in the positive electrode active material according to an embodiment of the present invention, the lithium composite metal oxide may be to include a compound of formula (1).
[화학식 1][Formula 1]
LiaNi1-x-yCoxM1yM2zO2 Li a Ni 1-xy Co x M1 y M2 z O 2
(상기 화학식 1에서, M1은 Al 및 Mn으로 이루어진 군에서 선택되는 어느 하나 또는 둘 이상의 원소를 포함하고, M2는 W, Mo Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, 및 Nb로 이루어진 군에서 선택되는 어느 하나 또는 둘 이상의 원소를 포함하고, 1.0≤a≤1.5, 0<x≤0.5, 0<y≤0.5, 0<z≤0.02, 0<x+y≤0.7인 것일 수 있으며, 보다 구체적으로는 1.0≤a≤1.2, 0<x≤0.5, 0<y≤0.5, 0.0005≤z≤0.02, 0<x+y≤0.7인 것일 수 있다)(In Formula 1, M1 includes any one or two or more elements selected from the group consisting of Al and Mn, M2 is W, Mo Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, It includes any one or two or more elements selected from the group consisting of Ca, and Nb, 1.0≤a≤1.5, 0 <x≤0.5, 0 <y≤0.5, 0 <z≤0.02, 0 <x + y≤ 0.7, more specifically, 1.0≤a≤1.2, 0 <x≤0.5, 0 <y≤0.5, 0.0005≤z≤0.02, 0 <x + y≤0.7)
또, 상기 양극활물질은 비표면적 및 양극 합제 밀도를 고려하여 3 내지 20㎛의 평균 입자 직경(D50)을 가질 수 있다. 양극활물질의 평균 입자 직경이 3㎛ 미만이면 양극활물질간 응집으로 인해 양극 합제내 분산성 저하의 우려가 있고, 20㎛를 초과할 경우 양극활물질의 기계적 강도 저하 및 비표면적의 저하의 우려가 있다. 또 그 특이적인 구조로 인한 율 특성 및 초기용량 특성의 개선 효과를 고려할 때 3 내지 15㎛의 평균 입자 직경(D50)을 갖는 것일 수 있다. 본 발명에 있어서, 상기 양극활물질의 평균 입자 직경(D50)은 입자 직경 분포의 50% 기준에서의 입자 직경으로 정의할 수 있다. 본 발명에 있어서, 상기 양극활물질의 평균 입자 직경(D50)은 예를 들어, 레이저 회절법(laser diffraction method)을 이용하여 측정할 수 있다. 예를 들어, 상기 양극활물질의 평균 입자 직경(D50)의 측정 방법은, 양극활물질의 입자를 분산매 중에 분산시킨 후, 시판되는 레이저 회절 입도 측정 장치(예를 들어 Microtrac MT 3000)에 도입하여 약 28 kHz의 초음파를 출력 60 W로 조사한 후, 측정 장치에 있어서의 입자 직경 분포의 50% 기준에서의 평균 입자 직경(D50)을 산출할 수 있다.In addition, the cathode active material may have an average particle diameter (D 50 ) of 3 to 20㎛ in consideration of the specific surface area and the positive electrode mixture density. If the average particle diameter of the positive electrode active material is less than 3 μm, there is a fear of dispersibility in the positive electrode mixture due to aggregation between the positive electrode active materials, and if it exceeds 20 μm, the mechanical strength of the positive electrode active material and the specific surface area may be reduced. In addition, when considering the effect of improving the rate characteristics and initial capacity characteristics due to the specific structure may have an average particle diameter (D 50 ) of 3 to 15㎛. In the present invention, the average particle diameter (D 50 ) of the positive electrode active material may be defined as the particle diameter at 50% of the particle diameter distribution. In the present invention, the average particle diameter (D 50 ) of the positive electrode active material can be measured using, for example, a laser diffraction method. For example, in the method for measuring the average particle diameter (D 50 ) of the positive electrode active material, the particles of the positive electrode active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000) and After irradiating an ultrasonic wave of 28 kHz with an output of 60 W, the average particle diameter (D 50 ) at a 50% reference of the particle diameter distribution in the measuring device can be calculated.
상기한 양극활물질(2a)은 양극활물질층(2) 총 중량에 대하여 80 내지 99 중량%로 포함될 수 있다. 양극활물질의 함량이 80 중량% 미만이면 전지의 용량 특성이 저하될 우려가 있고, 99 중량%를 초과할 경우 상대적으로 도전재의 함량 감소로 인해 양극활물질과 도전재의 접촉 확률 저하 및 이로 인한 전기적 비활성 활물질의 증가로 전지의 출력특성이 저하될 우려가 있다. The positive electrode active material 2a may be included in an amount of 80 to 99 wt% based on the total weight of the positive electrode active material layer 2. If the content of the positive electrode active material is less than 80% by weight, the capacity characteristics of the battery may be deteriorated. If the content of the positive electrode active material is higher than 99% by weight, the contact probability of the positive electrode active material and the conductive material is lowered due to the decrease of the content of the conductive material, and thus the electrically inactive active material. There is a possibility that the output characteristics of the battery may decrease due to the increase of.
또, 상기 제1 탄소 나노튜브(2b)는 복수 개의 탄소 나노튜브 단위체가 집합되어 형성된 2차 구조물로서, 복수 개의 탄소 나노튜브 단위체가 단위체 길이 방향의 축이 실질적으로 동일한 배향으로 나란하게 배열되어 다발(bundle) 혹은 로프(rope) 형태를 갖는 번들형이거나, 또는 상기 탄소 나노튜브 단위체가 뒤엉켜 있는 인탱글(entangle) 형태를 갖는 것일 수 있다. 이중에서도 우수한 분산성을 고려할 때 상기 제1 탄소 나노튜브는 번들형 일 수 있다.In addition, the first carbon nanotubes 2b are secondary structures formed by collecting a plurality of carbon nanotube units, and the plurality of carbon nanotube units are arranged side by side in substantially the same orientation in the longitudinal direction of the unit. The bundle may have a bundle or rope shape, or may have an entangle shape in which the carbon nanotube units are entangled. In consideration of excellent dispersibility, the first carbon nanotubes may be bundled.
통상 탄소 나노튜브는 탄소 나노튜브를 구성하는 단위체의 결정성과 구조 및 형태, 상기 단위체로 이루어진 2차 입자의 구조와 형태, 그리고 탄소 나노튜브내 포함된 금속원소의 함량 등에 따라 물성이 달라질 수 있다. 이에 따라 상기한 요인들 중 어느 하나 또는 둘 이상을 조합적으로 제어함으로써, 탄소 나노튜브의 용도에 따라 요구되는 물성을 갖도록 할 수 있다. 구체적으로, 탄소 나노튜브는 성장시 결정성이 높고, 결함(defect)이 적을수록 그리고 탄소 나노튜브를 형성하는 벽(wall)의 두께가 얇을수록 낮은 저항을 나타낼 수 있다. 또, 탄소 나노튜브 자체의 저항이 낮을수록 전극 제조에 적용시 전극내 저항을 낮출 수 있고, 그 결과 전지 성능을 향상시킬 수 있다. In general, the carbon nanotubes may have different physical properties depending on the crystallinity and structure and shape of the units constituting the carbon nanotubes, the structure and shape of the secondary particles composed of the units, and the content of metal elements included in the carbon nanotubes. Accordingly, by controlling any one or two or more of the above factors, it is possible to have the physical properties required according to the use of the carbon nanotubes. Specifically, the carbon nanotubes may exhibit low resistance as the crystallinity is high during growth, the defects are smaller, and the thickness of the walls forming the carbon nanotubes is thinner. In addition, the lower the resistance of the carbon nanotubes themselves, the lower the intra-electrode resistance when applied to electrode production, and as a result the battery performance can be improved.
본 발명에서 사용되는 상기 제1 탄소 나노튜브는 단일벽, 이중벽 및 다중벽의 탄소 나노튜브 단위체 중 어느 하나 또는 둘 이상을 포함할 수 있다.The first carbon nanotubes used in the present invention may include any one or two or more of single-walled, double-walled, and multi-walled carbon nanotube units.
또, 상기 제1 탄소 나노튜브는 단위체의 직경이 10 내지 100 nm이고, 길이가 3 내지 10 ㎛인 것일 수 있다. 제1 탄소 나노튜브 단위체가 상기한 직경 및 길이 조건을 충족할 때, 양극합제내 불균일 분산에 대한 우려 없이 전기전도성 네트워크 형성이 용이할 수 있다. The first carbon nanotubes may have a diameter of 10 to 100 nm and a length of 3 to 10 μm. When the first carbon nanotube unit meets the above diameter and length conditions, it may be easy to form an electrically conductive network without fear of non-uniform dispersion in the positive electrode mixture.
또, 상기 제1 탄소 나노튜브는 상기한 단위체의 직경 및 길이 조건과 함께, 2차 입자로서 비표면적이 20 내지 2000 m2/g인 것일 수 있다. 제1 탄소 나노튜브의 비표면적이 20 m2/g 미만이면 반응면적의 감소로 개선효과가 미미할 수 있고, 또 2000 m2/g를 초과하면 전도성 네트워크 형성이 어려울 수 있다. 보다 구체적으로, 제1 탄소 나노튜브의 비표면적 제어에 따른 개선효과의 현저함을 고려할 때, 상기 제1 탄소 나노튜브의 비표면적은 100 내지 400m2/g일 수 있다. In addition, the first carbon nanotubes may have a specific surface area of 20 to 2000 m 2 / g as secondary particles, together with the diameter and length conditions of the unit. If the specific surface area of the first carbon nanotube is less than 20 m 2 / g, the improvement may be insignificant due to the reduction of the reaction area, and if it exceeds 2000 m 2 / g, it may be difficult to form a conductive network. More specifically, considering the remarkable effect of the improvement according to the control of the specific surface area of the first carbon nanotubes, the specific surface area of the first carbon nanotubes may be 100 to 400m 2 / g.
본 발명에 있어서, 탄소 나노튜브의 비표면적은 BET 법에 의해 측정한 것으로서, 구체적으로는 BEL Japan 사 BELSORP-mino II를 이용하여 액체 질소 온도 하(77K)에서의 질소가스 흡착량으로부터 산출할 수 있다.In the present invention, the specific surface area of the carbon nanotubes is measured by the BET method, and specifically, it can be calculated from the nitrogen gas adsorption amount under the liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan. have.
또, 상기 제1 탄소 나노튜브는 0.01 내지 200kg/m3의, 보다 구체적으로는 0.01 내지 10 kg/m3, 보다 더 구체적으로는 0.01 내지 1 kg/m3의 벌크 밀도를 갖는 것일 수 있다. 탄소 나노튜브는 벌크밀도가 낮을수록 우수한 분산성을 나타낼 수 있으나, 벌크밀도가 지나치게 낮을 경우 전극내 탄소 나노튜브 단위체 양이 감소하여 전극 내 전기 전도성이 낮아질 수 있다. 본 발명에서 사용되는 제1 탄소 나노튜브는 상기한 범위의 벌크밀도를 가짐으로써 우수한 전기전도성을 나타낼 수 있다. 본 발명에 있어서, 탄소 나노튜브의 벌크 밀도는 하기 수학식 3에 따라 결정될 수 있다.In addition, the first carbon nanotube may have a bulk density of 0.01 to 200 kg / m 3 , more specifically 0.01 to 10 kg / m 3 , even more specifically 0.01 to 1 kg / m 3 . Carbon nanotubes may exhibit excellent dispersibility as the bulk density is low, but when the bulk density is too low, the amount of carbon nanotube units in the electrode may be reduced, thereby lowering the electrical conductivity in the electrode. The first carbon nanotubes used in the present invention may exhibit excellent electrical conductivity by having the bulk density in the above range. In the present invention, the bulk density of the carbon nanotubes may be determined according to Equation 3 below.
[수학식 3][Equation 3]
벌크 밀도(kg/m3) = 탄소 나노튜브 중량(kg)/탄소 나노튜브 부피(m3)Bulk density (kg / m 3 ) = carbon nanotube weight (kg) / carbon nanotube volume (m 3 )
상기와 같은 제1 탄소 나노튜브는 상업적으로 입수하여 사용될 수도 있고, 또는 직접 제조하여 사용될 수도 있다. 제조할 경우, 아크방전법, 레이저 증발법 또는 화학기상 증착법 등의 통상의 방법을 이용하여 제조될 수 있으며, 제조 과정에서의 촉매의 종류, 열처리 온도 및 불순물 제거 방법 등의 제어를 통해 상기한 물성을 구현할 수 있다.Such first carbon nanotubes may be obtained commercially, or may be manufactured and used directly. In the case of manufacturing, the method may be manufactured using a conventional method such as an arc discharge method, a laser evaporation method or a chemical vapor deposition method, and the aforementioned physical properties may be controlled by controlling the type of catalyst, heat treatment temperature, and impurity removal method in the manufacturing process. Can be implemented.
상기 제1 탄소 나노튜브는 양극활물질층 총 중량에 대하여 0.2 내지 2 중량%로 포함될 수 있다. 제1 탄소 나노튜브의 함량이 0.2 중량% 미만이면 양극내 전도성 저하 및 저항 증가로 출력 특성이 저하될 우려가 있고, 2 중량%를 초과할 경우, 탄소 나노튜브의 분산이 어렵고 전극내 기공을 막아 전해액 내 Li 전달 저항 증가로 출력 특성이 저하될 우려가 있다. The first carbon nanotubes may be included in an amount of 0.2 to 2 wt% based on the total weight of the cathode active material layer. If the content of the first carbon nanotube is less than 0.2% by weight, there is a possibility that the output characteristics may decrease due to the decrease in conductivity and resistance in the anode. There is a fear that the output characteristics may decrease due to an increase in the Li transfer resistance in the electrolyte.
또, 상기 양극활물질층(2)은 상기한 제1 탄소 나노튜브와 함께 입자상, 섬유상 또는 판상 등의 서로 다른 형상을 갖는 이종의 도전재(미도시)를 더 포함할 수 있으며, 구체적으로는 양극활물질층 총 중량에 대하여 0.2 내지 6 중량%로 더 포함할 수 있다. 이와 같이 형상 이방성을 갖는 도전재가 추가 사용될 경우, 양극활물질 및 전해질과의 삼상 계면 형성이 용이하여 반응성이 증가되고, 또 양극활물질간의 도전성을 확보하면서도 양극활물질 사이의 공극을 유지하도록 하여 우수한 기공 특성을 갖도록 할 수 있다.In addition, the cathode active material layer 2 may further include a heterogeneous conductive material (not shown) having a different shape such as particulate, fibrous or plate together with the first carbon nanotubes described above. It may further comprise 0.2 to 6% by weight based on the total weight of the active material layer. When a conductive material having a shape anisotropy is used as described above, it is easy to form a three-phase interface between the positive electrode active material and the electrolyte, thereby increasing the reactivity. Also, while maintaining conductivity between the positive electrode active materials, the pores between the positive electrode active materials can be maintained to provide excellent pore characteristics. You can have it.
상기 추가로 포함되는 도전재가 입자상 도전재인 경우, 구체적으로 평균 입자 직경(D50)이 10 내지 150 nm이고, 비표면적이 20 내지 600 m2/g인 것일 수 있다. 상기한 범위 조건을 충족하는 작은 입자 크기와 넓은 비표면적을 가짐으로써, 양극활물질과 전해질과의 삼상 계면에 있어서의 전자 공급성을 높여 반응성을 향상시킬 수 있다. 만약 입자상 도전재의 평균 입자 직경이 10nm 미만이거나, 비표면적이 170m2/g를 초과하면 입자상 도전재끼리의 응집으로 양극 합제내 분산성이 크게 저하되고, 또 평균 입자 직경이 45nm를 초과하거나 또는 비표면적인 40m2/g 미만이면 그 크기가 지나치게 크기 때문에 양극활물질의 공극률에 따른 도전재 배치에 있어서 양극 합제 전체에 걸쳐 균일하게 분산되지 않고 부분적으로 편중될 수 있다. 상기 입자상 도전재의 평균 입자 직경은 앞서 양극활물질에서와 동일한 방법으로 측정될 수 있다.When the additionally included conductive material is a particulate conductive material, specifically, the average particle diameter (D 50 ) may be 10 to 150 nm, and the specific surface area may be 20 to 600 m 2 / g. By having a small particle size and a wide specific surface area which satisfy | fill the above-mentioned range conditions, the reactivity can be improved by raising the electron supply property in the three-phase interface of a positive electrode active material and electrolyte. If the average particle diameter of the particulate conductive material is less than 10 nm or the specific surface area exceeds 170 m 2 / g, agglomeration of the particulate conductive materials greatly reduces the dispersibility in the positive electrode mixture, and the average particle diameter exceeds 45 nm or the ratio If the surface area is less than 40 m 2 / g, since the size is excessively large, in the conductive material arrangement according to the porosity of the positive electrode active material, it may be partially biased without being uniformly dispersed throughout the positive electrode mixture. The average particle diameter of the particulate conductive material may be measured in the same manner as in the cathode active material.
상기 입자상 도전재는 도전성을 갖는 동시에 그 형태적 조건을 충족하는 경우라면 특별한 제한 없이 사용 가능하지만, 입자상 도전재의 사용에 따른 개선 효과의 우수함을 고려할 때, 상기 입자상 도전재는 비흑연계의 탄소물질일 수 있다. 구체적으로, 상기 입자상 도전재는 카본 블랙, 아세틸렌 블랙, 케첸 블랙, 채널 블랙, 퍼네이스 블랙, 램프 블랙, 서멀 블랙, 또는 덴카 블랙 등일 수 있으며, 이중에서 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다.The particulate conductive material may be used without particular limitation as long as it has conductivity and meets its morphological conditions. However, the particulate conductive material may be a non-graphite carbon material in consideration of the excellent improvement effect of using the particulate conductive material. . Specifically, the particulate conductive material may be carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or denka black, and any one or a mixture of two or more thereof may be used.
또, 도전재에 있어서, 상기 판상 도전재는 서로 대응하는 두 면이 편평하고, 수평방향의 크기가 수직 방향의 크기보다 큰 입단(aggregate) 구조를 갖는 도전재로서, 완전한 판상 형상은 물론 판상과 유사한 형상인 플레이크(flake)상, 비늘상 등도 포함할 수 있다. 구체적으로, 상기 판상 도전재는 편평한 면에서의 직경과 판상의 두께 대비( = 직경/두께)이 2 내지 400인 것일 수 있다. 상기한 범위의 크기를 갖는 판상 도전재는 상기한 입자상 및 섬유상 도전재와의 혼합 사용시, 양극 합제 내 도전성 네트워크의 형성이 용이하고, 기공 특성을 잘 유지할 수 있다. 보다 구체적으로, 판상 도전재의 혼합 사용 및 그 입자크기의 제어에 따른 효과의 현저함을 고려할 때, 상기 판상 도전재는 두께에 대한 편평한 면에서의 직경의 비율이 10 내지 200인 것일 수 있다. 본 발명에 있어서, 판상형 도전재의 "직경"이란 편평한 면의 둘레가 이루는 폐곡선(closed curve)에서의 두 점을 연결한 선의 길이 중 가장 긴 길이를 의미한다. 이때 "폐곡선"이란 곡선 위의 한 점이 한 방향으로 움직여 다시 출발점으로 되돌아오는 곡선을 의미한다. 또, 판상형 도전재의 "두께"란 두 편평한 면 사이의 평균 길이를 의미한다.Further, in the conductive material, the plate-shaped conductive material is a conductive material having an aggregate structure in which two surfaces corresponding to each other are flat and the size in the horizontal direction is larger than the size in the vertical direction, and of course, the plate-like conductive material is similar to the plate shape. Flakes, scales, and the like, which are shaped, may also be included. In detail, the plate-shaped conductive material may have a diameter (= diameter / thickness) of 2 to 400 in diameter and a plate thickness on a flat surface. The plate-like conductive material having a size in the above range can easily form a conductive network in the positive electrode mixture when mixed with the above-mentioned particulate and fibrous conductive materials, and can maintain the pore characteristics well. More specifically, in consideration of the significant use of the mixed use of the plate-like conductive material and the effect of the control of the particle size, the plate-like conductive material may be a ratio of the diameter in the flat plane to the thickness of 10 to 200. In the present invention, the "diameter" of a plate-shaped conductive material means the longest length of the line which connected the two points in the closed curve which the perimeter of a flat surface makes. In this case, the "closed curve" means a curve in which a point on the curve moves in one direction and returns to the starting point. In addition, the "thickness" of a plate-shaped electrically conductive material means the average length between two flat surfaces.
또, 상기 양극활물질층(2)은 필요에 따라 양극활물질 입자들 간의 부착 및 양극활물질과 양극 집전체와의 접착력을 향상을 위해 바인더(미도시)를 더 포함할 수 있다.In addition, the cathode active material layer 2 may further include a binder (not shown) to improve adhesion between the cathode active material particles and adhesion between the cathode active material and the cathode current collector, as necessary.
상기 바인더는 구체적으로 폴리비닐리덴플루오라이드(PVDF), 비닐리덴플루오라이드-헥사플루오로프로필렌 코폴리머(PVDF-co-HFP), 폴리비닐알코올, 폴리아크릴로니트릴(polyacrylonitrile), 카르복시메틸셀룰로우즈(CMC), 전분, 히드록시프로필셀룰로우즈, 재생 셀룰로우즈, 폴리비닐피롤리돈, 테트라플루오로에틸렌, 폴리에틸렌, 폴리프로필렌, 에틸렌-프로필렌-디엔 폴리머(EPDM), 술폰화-EPDM, 스티렌 부타디엔 고무(SBR), 불소 고무, 또는 이들의 다양한 공중합체 등을 들 수 있으며, 이들 중 1종 단독 또는 2종 이상의 혼합물이 사용될 수 있다. 상기 바인더는 양극활물질층 총 중량에 대하여 1 내지 10 중량%로 포함될 수 있다.The binder is specifically polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene Butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, and the like, and one or more of these may be used. The binder may be included in an amount of 1 to 10% by weight based on the total weight of the positive electrode active material layer.
상기한 구성을 갖는 양극활물질층(2)은 양극활물질(2a) 입자간 그리고 상기 양극활물질(2a)과 제1 탄소 나노튜브(2b) 사이에 존재하는 복수 개의 공극을 포함하여 다공성을 나타낸다. 이와 같이 양극활물질층 내부에 형성된 공극은 전해질 등의 물질 이동의 통로가 되어 양극활물질층내 물질 전달 저항을 감소시킬 수 있다. The positive electrode active material layer 2 having the above-described configuration exhibits porosity including a plurality of pores existing between the particles of the positive electrode active material 2a and between the positive electrode active material 2a and the first carbon nanotubes 2b. As such, the voids formed inside the positive electrode active material layer may be a passage for mass transfer of an electrolyte or the like to reduce the mass transfer resistance in the positive electrode active material layer.
구체적으로 상기 양극활물질층(2)은 양극활물질층을 구성하는 구성성분의 물성 및 함량 제어를 통해 10 부피% 내지 50 부피%의 기공도(porosity), 보다 구체적으로는 20 부피% 내지 45 부피%의 기공도를 가질 수 있다.Specifically, the positive electrode active material layer 2 has a porosity of 10% by volume to 50% by volume, more specifically 20% by volume to 45% by volume, by controlling the properties and contents of the components constituting the positive electrode active material layer. It may have a porosity of.
또, 본 발명의 일 실시예에 따른 이차전지용 양극(10)에 있어서, 도전층(3)은 상기 양극활물질층(2)의 표면 상에 위치하며, 복수 개의 제2 탄소 나노튜브(3a)들이 서로 엉켜 3차원적으로 연결된 다공성 망상 구조체를 포함한다 (도 1a 및 1b 참조). 이때 제2 탄소나노튜브(3a)는 상술한 양극활물질층에 포함된 제1 탄소나노튜브에 대해 설명한 바와 같으며, 제1 탄소나노튜브와 동일하거나, 또는 상이할 수 있다. 구체적으로, 양극내 위치에 따른 기능적 차이를 고려할 때 상기 제2 탄소 나노튜브는 제1 탄소나노튜브에 비해 직경은 작고, 길이가 긴 것일 수 있다. In addition, in the secondary battery positive electrode 10 according to an embodiment of the present invention, the conductive layer 3 is located on the surface of the positive electrode active material layer 2, a plurality of second carbon nanotubes (3a) Intertwined three-dimensionally connected porous network structures (see FIGS. 1A and 1B). In this case, the second carbon nanotubes 3a may be the same as the first carbon nanotubes included in the cathode active material layer, and may be the same as or different from the first carbon nanotubes. Specifically, the second carbon nanotubes may have a smaller diameter and a longer length than the first carbon nanotubes when considering functional differences according to positions in the anode.
도 2a은 종래 탄소 나노튜브를 이용하여 제조한 양극의 단면 구조를 개략적으로 나타낸 모식도이고, 도 2b는 상기 양극 표면을 개략적으로 나타낸 평면도이다. 도 2a 및 도 2b에 나타난 바와 같이, 종래의 양극(100)의 경우, 탄소 나노튜브(12b)가 양극활물질층(12) 내부에 분포되어 있기 때문에, 양극 집전체(11)와의 접촉 부위에서는 전기 전도성을 유지할 수 있지만, 양극활물질층(12)의 표면으로 갈수록 탄소 나노튜브(12b)와의 접촉 확률이 낮아져 전기적 비활성 양극활물질(12a)이 존재하게 된다. 이와 같은 전지적 비활성 양극활물질(12a)은 전지 용량을 저하시키는 원인이 된다. 이러한 단점을 개선하기 위하여, 도전층 슬러리를 도포하여 양극활물질층 표면에 도전층을 추가로 형성하는 경우 (미도시), 양극활물질의 두께비 대비 0.02 이하의 얇은 두께의 도전층을 형성하기 쉽지 않지 않을 뿐만 아니라, 양극활물질 표면이 도전층으로 전부 덮여 있기 때문에, 전해액 내의 Li 이온이 전극으로의 이동이 원할하지 않아, 율 특성이 저하될 수 있다.Figure 2a is a schematic diagram showing a cross-sectional structure of the anode prepared using a conventional carbon nanotube, Figure 2b is a plan view schematically showing the surface of the anode. As shown in FIG. 2A and FIG. 2B, in the case of the conventional anode 100, since the carbon nanotubes 12b are distributed inside the cathode active material layer 12, at the contact portion with the cathode current collector 11, Although the conductivity can be maintained, the contact probability with the carbon nanotubes 12b is lowered toward the surface of the cathode active material layer 12, so that the electrically inactive cathode active material 12a is present. Such battery inert positive electrode active material 12a causes a decrease in battery capacity. In order to improve this disadvantage, when the conductive layer is further formed by applying the conductive layer slurry (not shown), it may not be easy to form a conductive layer having a thin thickness of 0.02 or less relative to the thickness ratio of the positive electrode active material. In addition, since the surface of the positive electrode active material is entirely covered with the conductive layer, Li ions in the electrolyte are not desired to move to the electrode, and the rate characteristic may be lowered.
반면, 도 1a 및 도 1b에 나타난 바와 같이, 본 발명의 일 실시예에 따른 양극(10)은 상기 제2 탄소 나노튜브(3a)로 이루어진 다공성 망상 구조체를 포함하는 도전층(3)이 양극활물질층(2) 표면에 위치함으로써(도 4 참조), 양극활물질층 표면상에 존재하는 양극활물질(2a)과의 접촉을 통해 비활성 양극활물질의 발생을 방지하고, 동시에 양극활물질층 내부에 존재하는 제1 탄소 나노튜브(2b)와 연결되어 전기적 도전성 경로를 형성함으로써, 양극활물질층 내에서의 전자 전달 저항을 저하시킬 수 있다.On the other hand, as shown in Figures 1a and 1b, the positive electrode 10 according to an embodiment of the present invention is a positive electrode active material is a conductive layer 3 including a porous network structure consisting of the second carbon nanotubes (3a) By being located on the surface of the layer 2 (see FIG. 4), the inert positive electrode active material is prevented from being generated through contact with the positive electrode active material 2a present on the surface of the positive electrode active material layer, and at the same time, By connecting to the one carbon nanotube (2b) to form an electrically conductive path, it is possible to reduce the electron transfer resistance in the positive electrode active material layer.
상기한 다공성 망상 구조체를 포함하는 도전층(3)은 양극활물질층(2)의 두께에 대하여 적어도 1:001 내지 1:0.05의 두께비로 형성될 수 있다. 도전층의 두께가 0.001 두께비 미만이면 양극활물질층 위에 탄소 나노튜브 네트워크가 충분하게 형성되지 못 할 우려가 있고, 두께가 0.05를 초과하면 형성된 탄소나노튜브 네트워크 내 기공이 막힐 우려가 있다. 구체적으로, 상기 도전층(3) : 양극활물질층(2)의 두께비는 0.001 내지 0.01 : 1인 것이 바람직하며, 보다 더 구체적으로는 0.001 내지 0.005의 두께비로 형성될 수 있다. 이때, 본 발명의 도전층이 양극활물질층이 두께 대비 1: 0.02 내지 0.05 두께로 형성되는 경우에도, 종래 기술과 달리 양극활물질층 표면에 망상 구조체로 형성되기 때문에, 전해액 내의 Li 이온이 전극으로 이동하기 원할하여, 율 특성이 종래 대비 보다 향상될 수 있다.The conductive layer 3 including the porous network structure may be formed at a thickness ratio of at least 1: 001 to 1: 0.05 with respect to the thickness of the cathode active material layer 2. If the thickness of the conductive layer is less than 0.001 thickness ratio, the carbon nanotube network may not be sufficiently formed on the positive electrode active material layer, and if the thickness exceeds 0.05, pores in the formed carbon nanotube network may be blocked. Specifically, the thickness ratio of the conductive layer 3 to the cathode active material layer 2 is preferably 0.001 to 0.01: 1, and more specifically, may be formed in a thickness ratio of 0.001 to 0.005. At this time, even when the positive electrode active material layer of the present invention is formed to a thickness of 1: 0.02 to 0.05 compared to the thickness, since the structure is formed as a network structure on the surface of the positive electrode active material layer, unlike the prior art, Li ions in the electrolyte move to the electrode To be desired, the rate characteristic can be improved over the prior art.
또, 상기 도전층(3)에 포함된 제2 탄소 나노튜브(3a)는 최종 제조되는 양극 중에 포함되는 전체 탄소 나노튜브의 함량을 고려하여 결정될 수 있으며, 구체적으로 양극 중의 전체 탄소 나노튜브의 함량의 4배를 초과하지 않도록 포함될 수 있다. 만약, 양극 중에 전체 탄소 나노튜브 함량이 4배를 초과하는 경우, 도전층의 두께 증가로 활물질층 내로의 전해액 전달을 방해하여 저항이 증가할 수 있다.In addition, the second carbon nanotubes 3a included in the conductive layer 3 may be determined in consideration of the content of the total carbon nanotubes included in the final anode, and specifically, the content of the total carbon nanotubes in the anode It may be included so as not to exceed four times. If the total carbon nanotube content in the positive electrode exceeds 4 times, increasing the thickness of the conductive layer may interfere with the transfer of the electrolyte into the active material layer, thereby increasing resistance.
이때, 상기 제1 탄소 나노튜브 : 제2 탄소 나노튜브는 1 : 0.08 내지 0.42 중량 비율로 포함될 수 있다. In this case, the first carbon nanotubes: the second carbon nanotubes may be included in a weight ratio of 1: 0.08 to 0.42.
상기 제2 탄소 나노튜브의 중량비가 0.08 미만이면 양극활물질층 위에 탄소 나노튜브 네트워크가 충분하게 형성되지 못 할 수 있고, 0.42를 초과하면 제2 탄소나노튜브에 의해 형성되는 3차원 네트워크 구조 내부의 기공도가 낮아져 물질 전달 효과가 감소할 수 있다.If the weight ratio of the second carbon nanotube is less than 0.08, the carbon nanotube network may not be sufficiently formed on the positive electrode active material layer, and if it exceeds 0.42, the pores inside the three-dimensional network structure formed by the second carbon nanotube The degree can be lowered and the mass transfer effect can be reduced.
또, 상기 제2 탄소 나노튜브(3a)의 다공성 망상 구조체는 구조체 내 제2 탄소나노튜브 사이의 공극을 포함한다. 이는 제2 탄소 나노튜브의 직경 및 함량 등의 제어를 통해 다공성 망상 구조체내 공극의 크기 및 기공도를 제어할 수 있는데, 구체적으로 상기 다공성 망상 구조체를 포함하는 도전층(3)은 양극활물질층(2)내 기공도 보다 높은 기공도를 갖는다. 이와 같이 보다 높은 기공도를 가짐으로써 물질 전달 저항의 증가를 방지할 수 있다. 구체적으로, 상기 도전층(3)의 기공도는 양극활물질(2)층내 기공도 보다 + 10% 이상 더 가질 수 있다. 보다 구체적으로는 상기 도전층의 기공도는 20 부피% 내지 60 부피%의 기공도, 보다 구체적으로 30 부피% 내지 60 부피%를 가질 수 있다.In addition, the porous network structure of the second carbon nanotubes 3a includes pores between the second carbon nanotubes in the structure. This may control the size and porosity of the pores in the porous network structure by controlling the diameter and content of the second carbon nanotubes. 2) Porosity is higher than porosity. Thus, having a higher porosity can prevent an increase in mass transfer resistance. Specifically, the porosity of the conductive layer 3 may have + 10% or more more than the porosity in the positive electrode active material 2 layer. More specifically, the porosity of the conductive layer may have a porosity of 20% by volume to 60% by volume, and more specifically 30% by volume to 60% by volume.
보다 구체적으로, 양극 전체에 걸친 전기적 네트워크의 충분한 형성으로 전하 전달 저항을 감소시키고, 또 양극활물질층과 도전층 사이의 기공도 제어를 통해 물질 저항을 감소시킴으로써 전지의 출력 특성을 더욱 향상시키기 위해, 본 발명의 일 실시예에 따른 이차전지용 양극에 있어서, 상기 양극활물질층은 양극활물질층 총 부피에 대해 10 내지 50 부피%의 기공도를 가지며, 상기 도전층의 두께는 양극활물질층 전체 두께를 기준으로 0.001 내지 0.05 : 1이고, 상기 도전층의 기공도는 양극활물질층의 보다 10 부피% 이상 높은 기공도를 가질 수 있다. 보다 구체적으로, 본 발명의 일 실시예에 따른 이차전지용 양극에 있어서, 상기 양극활물질층은 양극활물질층 총 부피에 대해 10 내지 50 부피%의 기공도를 가지며, 상기 도전층의 두께는 양극활물질층 전체 두께를 기준으로 0.001 내지 0.01 : 1이고, 상기 도전층의 기공도는 20 부피% 내지 60 부피% 이상일 수 있다.More specifically, in order to further improve the output characteristics of the battery by reducing the charge transfer resistance with sufficient formation of the electrical network throughout the anode, and by reducing the material resistance through porosity control between the cathode active material layer and the conductive layer, In the positive electrode for a secondary battery according to an embodiment of the present invention, the cathode active material layer has a porosity of 10 to 50% by volume based on the total volume of the cathode active material layer, and the thickness of the conductive layer is based on the total thickness of the cathode active material layer. To 0.001 to 0.05: 1, the porosity of the conductive layer may have a porosity of 10% by volume or more higher than the positive electrode active material layer. More specifically, in the positive electrode for a secondary battery according to an embodiment of the present invention, the positive electrode active material layer has a porosity of 10 to 50% by volume with respect to the total volume of the positive electrode active material layer, the thickness of the conductive layer is a positive electrode active material layer 0.001 to 0.01: 1 based on the total thickness, and the porosity of the conductive layer may be 20% by volume to 60% by volume or more.
상기한 바와 같은 구조를 갖는 본 발명의 일 실시예에 따른 이차전지용 양극은, A secondary battery positive electrode according to an embodiment of the present invention having a structure as described above,
제2 탄소 나노튜브를 분산매 중에 첨가하여 분산매의 표면 상에 제2 탄소 나노튜브 막이 형성된 도전층 형성용 조성물을 준비하는 단계(단계 1); Adding a second carbon nanotube to the dispersion medium to prepare a composition for forming a conductive layer on which a second carbon nanotube film is formed on the surface of the dispersion medium (step 1);
양극 집전체의 적어도 일면에, 양극활물질 및 제1 탄소 나노튜브를 포함하는 양극활물질층이 형성된 전극 조립체를 상기 도전층 형성용 조성물에 함침한 후 상기 제2 탄소 나노튜브 막이 양극활물질층 표면 상에 위치하도록 전극 조립체를 들어올려 도전층을 형성하는 단계(단계 2);를 포함하는 제조방법에 의해 제조될 수 있다.After impregnating the electrode assembly having a positive electrode active material layer including a positive electrode active material and a first carbon nanotube on at least one surface of the positive electrode current collector in the conductive layer forming composition, the second carbon nanotube film is formed on the surface of the positive electrode active material layer. Lifting the electrode assembly to position to form a conductive layer (step 2) can be manufactured by a manufacturing method comprising a.
이에 따라 본 발명의 또 다른 일 실시예에 따르면 상기 이차전지용 양극의 제조방법이 제공된다.Accordingly, according to another embodiment of the present invention, a method of manufacturing the positive electrode for a secondary battery is provided.
도 3은 본 발명의 일 실시예에 따른 이차전지용 양극의 제조방법을 개략적으로 나타낸 공정도이다. 도 3은 본 발명을 설명하기 위한 일 예일뿐 본 발명이 이에 한정되는 것은 아니다. 이하 도 3을 참고하여 각 단계별로 설명한다. 3 is a process diagram schematically showing a method of manufacturing a cathode for a secondary battery according to an embodiment of the present invention. 3 is only an example for describing the present invention and the present invention is not limited thereto. Hereinafter, each step will be described with reference to FIG. 3.
먼저, 상기 이차전지용 양극의 제조를 위한 단계 1은 도전층 형성용 조성물을 준비하는 단계이다(S1).First, step 1 for manufacturing the secondary battery positive electrode is a step of preparing a composition for forming a conductive layer (S1).
상기 도전층 형성용 조성물은 탄소 나노튜브를 분산매 중에 첨가함으로써 제조될 수 있는데, 구체적으로 탄소 나노튜브가 분산매 중에 혼합되지 않고, 분산매 표면 상에 3차원 다공성 망상 구조체 막을 형성할 수 있도록 분산매 상에 제2 탄소 나노튜브를 조금씩 적하한 다음, 초음파 분산(sonication) 처리를 통해 분산매 상에서 제2 탄소나노튜브를 분산시켜 제조할 수 있다.The conductive layer forming composition may be prepared by adding carbon nanotubes to a dispersion medium. Specifically, the carbon nanotubes may not be mixed in the dispersion medium, and may be formed on the dispersion medium to form a three-dimensional porous network film on the surface of the dispersion medium. 2 carbon nanotubes are added dropwise, and then the second carbon nanotubes are dispersed on a dispersion medium by ultrasonic dispersion.
이때, 상기 제2 탄소 나노튜브는 앞서 설명한 제1 탄소 나노튜브와 동일한 것일 수 있으며, 그 첨가량은 최종 제조되는 도전층의 두께 및 양극 활물질 중의 탄소 나노튜브의 전체 함량을 고려하려 적절히 결정될 수 있다.In this case, the second carbon nanotubes may be the same as the first carbon nanotubes described above, and the amount of the second carbon nanotubes may be appropriately determined in consideration of the thickness of the conductive layer to be finally manufactured and the total content of the carbon nanotubes in the positive electrode active material.
또, 상기 분산매로는 디메틸포름아미드(DMF), 디에틸 포름아미드, 디메틸 아세트아미드(DMAc), N-메틸 피롤리돈(NMP) 등의 아미드계 극성 유기 용매; 메탄올, 에탄올, 1-프로판올, 2-프로판올(이소프로필 알코올), 1-부탄올(n-부탄올), 2-메틸-1-프로판올(이소부탄올), 2-부탄올(sec-부탄올), 1-메틸-2-프로판올(tert-부탄올), 펜탄올, 헥사놀, 헵탄올 또는 옥탄올 등의 알코올류; 에틸렌글리콜, 디에틸렌글리콜, 트리에틸렌 글리콜, 프로필렌 글리콜, 1,3-프로판디올, 1,3-부탄디올, 1,5-펜탄디올, 또는 헥실렌글리콜 등의 글리콜류; 글리세린, 트리메티롤프로판, 펜타에리트리톨, 또는 소르비톨 등의 다가 알코올류; 에틸렌글리콜 모노메틸에테르, 디에틸렌글리콜 모노메틸에테르, 트리에틸렌글리콜 모노메틸에테르, 테트라에틸렌글리콜 모노 메틸에테르, 에틸렌글리콜 모노에틸에테르, 디에틸렌글리콜 모노에틸에테르, 트리에틸렌글리콜 모노에틸에테르, 테트라에틸렌글리콜 모노에틸에테르, 에틸렌글리콜 모노부틸에테르, 디에틸렌글리콜 모노부틸에테르, 트리에틸렌글리콜 모노부틸에테르, 또는 테트라에틸렌글리콜 모노부틸에테르 등의 글리콜 에테르류; 아세톤, 메틸 에틸 케톤, 메틸프로필 케톤, 또는 사이클로펜타논 등의 케톤류; 초산에틸, γ-부틸 락톤, 및 ε-프로피오락톤 등의 에스테르류 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다. 이중에서도 상기 탄소나노튜브 막 형성시의 퍼짐성을 고려하여 적절한 극성차를 갖는 분산매를 선택할 수 있으며, 보다 구체적으로는 알코올류의 용매가 사용될 수 있다.Moreover, as said dispersion medium, Amide type polar organic solvent, such as dimethylformamide (DMF), diethyl formamide, dimethyl acetamide (DMAc), N-methyl pyrrolidone (NMP); Methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl Alcohols such as 2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol; Glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; Polyhydric alcohols such as glycerin, trimetholpropane, pentaerythritol, or sorbitol; Ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol mono methyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol Glycol ethers such as monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; Ketones such as acetone, methyl ethyl ketone, methylpropyl ketone, or cyclopentanone; Ester, such as ethyl acetate, (gamma) -butyl lactone, (epsilon) -propiolactone, etc. are mentioned, Any one or a mixture of two or more of these may be used. Among them, a dispersion medium having an appropriate polarity difference may be selected in consideration of the spreadability in forming the carbon nanotube film, and more specifically, an alcohol solvent may be used.
다음으로, 단계 2는, 상기 단계 1에서 제조한 도전층 형성용 조성물을 이용하여 양극활물질층 상에 도전층을 형성하는 단계이다(S2).Next, step 2 is a step of forming a conductive layer on the cathode active material layer using the composition for forming a conductive layer prepared in step 1 (S2).
구체적으로는 양극 집전체 상에 양극활물질층을 형성하여 양극 조립체를 제조한 후, 상기 단계 1에서 제조한 도전층 형성용 조성물 중에 함침한 다음, 양극조립체의 활물질층 상에 탄소나노튜브 막이 위치하도록 서서히 들어올림으로써 수행될 수 있다. Specifically, a cathode active material layer is formed on a cathode current collector to prepare a cathode assembly, and then impregnated in the composition for forming a conductive layer prepared in Step 1, so that the carbon nanotube film is positioned on the active material layer of the cathode assembly. This can be done by lifting slowly.
상기 양극 조립체는 양극활물질, 탄소나노튜브 그리고 선택적으로 바인더를 용매중에서 혼합하여 양극활물질층 형성용 조성물을 제조하고, 이를 양극 집전체의 적어도 일면에 도포하고 건조하거나, 또는 상기 양극활물질층 형성용 조성물을 별도의 지지체상에 캐스팅한 후 이 지지체로부터 박리하여 얻은 필름을 양극 집전체 상에 라미네이션함으로써 제조될 수 있다. 이때 상기 양극조립체, 양극활물질, 탄소나노튜브 및 바인더의 종류 및 함량은 앞서 설명한 바와 동일하다.The positive electrode assembly is a positive electrode active material, carbon nanotubes and optionally a binder in a solvent to prepare a composition for forming a positive electrode active material layer, it is applied to at least one surface of the positive electrode current collector and dried, or the composition for forming the positive electrode active material layer Can be prepared by casting a film on a separate support and then laminating the film obtained by peeling from the support on a positive electrode current collector. In this case, the type and content of the cathode assembly, the cathode active material, the carbon nanotubes and the binder are the same as described above.
상기 용매로는 당해 기술분야에서 일반적으로 사용되는 용매일 수 있으며, 디메틸셀폭사이드(dimethyl sulfoxide, DMSO), 이소프로필 알코올(isopropyl alcohol), N-메틸피롤리돈(NMP), 아세톤(acetone) 또는 물 등을 들 수 있으며, 이들 중 1종 단독 또는 2종 이상의 혼합물이 사용될 수 있다. 상기 용매의 사용량은 조성물의 도포 두께, 제조 수율을 고려하여 상기 전극 활물질 및 바인더를 용해 또는 분산시키고, 이후 전극 제조를 위한 도포시 우수한 두께 균일도를 나타낼 수 있는 점도를 갖도록 하는 정도면 충분하다.The solvent may be a solvent generally used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or acetone. Water, and the like, one of these alone or a mixture of two or more thereof may be used. The amount of the solvent may be sufficient to dissolve or disperse the electrode active material and the binder in consideration of the coating thickness of the composition and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity during application for electrode production.
상기와 같은 방법으로 제조된 양극조립체를 단계 1에서 제조한 도전층 형성용 조성물 중에 함침시킨 후, 도전층 형성용 조성물의 표면 상에 위치하는 제2 탄소나노튜브 막을 양극활물질층 위로 걷어 올린다. 이와 같은 공정을 통해 도전층 형성용 조성물의 표면상에 떠 있는 얇은 탄소나노튜브 막을 그대로 양극활물질층 위에 형성시킬 수 있다.After impregnating the positive electrode assembly prepared by the above method in the conductive layer forming composition prepared in step 1, the second carbon nanotube film located on the surface of the conductive layer forming composition is rolled up on the positive electrode active material layer. Through this process, a thin carbon nanotube film floating on the surface of the conductive layer forming composition may be formed on the cathode active material layer as it is.
이때, 함침 시간은 대략 10초 내지 60초 일 수 있으며, 60초를 초과하는 경우 양극 활물질 내 바인더를 변형시켜 구조 변화를 일으킬 수 있다. 또한, 대략 0.13 m/min 내지 0.16 m/min, 구체적으로 0.15 m/min의 속도로 서서히 양극활물질층을 들어 올릴 수 있다.In this case, the impregnation time may be approximately 10 seconds to 60 seconds, and if it exceeds 60 seconds, the binder in the positive electrode active material may be modified to cause a structural change. In addition, the cathode active material layer may be gradually lifted at a speed of approximately 0.13 m / min to 0.16 m / min, specifically 0.15 m / min.
이때, 본 발명의 방법은 탄소나노튜브 막 중에 존재하는 분산매를 증발 제거하기 위하여, 5 내지 20 pa, 60℃ 내지 90℃ 온도에서 5 내지 7 시간 동안, 구체적으로 10 pa, 80℃ 온도에서 6 시간 동안 건조 단계(S3)를 선택적으로 수행할 수 있다.At this time, the method of the present invention, for 5 to 7 hours at 5 to 20 pa, 60 ℃ to 90 ℃ temperature, specifically 10 pa, 80 ℃ temperature for 6 hours to evaporate the dispersion medium present in the carbon nanotube film During drying step S3 can optionally be carried out.
이와 같은 방법으로 형성할 경우, 종래 도전층 슬러리를 도포하는 방법으로 도전층을 형성하는 경우에 비해 보다 얇은 두께의 도전층의 형성이 가능하며, 그 결과, 도전층내 물질 전달 저항 증가를 방지할 수 있다. When formed in this manner, it is possible to form a conductive layer having a thinner thickness than in the case of forming a conductive layer by applying a conductive layer slurry, and as a result, it is possible to prevent an increase in mass transfer resistance in the conductive layer. have.
즉, 상기한 방법에 따라 제조되는 본 발명의 양극은, 양극활물질층 상에 탄소 나노튜브의 다공성 망목 구조체를 포함하는 도전층이 위치하고, 상기 도전층내 탄소 나노튜브가 양극활물질층내 탄소 나노튜브와 연결되어 도전 경로를 형성함으로써, 종래 양극활물질층의 형성시 탄소 나노튜브를 혼합 사용하는 경우 및 양극활물질 표면을 탄소 나노튜브로 코팅하여 사용하는 경우에 비해 동량의 탄소 나노튜브 사용시 현저히 개선된 저항 감소 및 이에 따른 전지 출력 특성 개선 효과를 나타낼 수 있다. 상세하게는 종래 양극활물질층 형성시 탄소 나노튜브를 혼합 사용하는 경우, 활물질층 표면에서의 탄소 나노튜브 함량 감소로 양극활물질과의 접촉 확률 저하 및 이에 따른 전지 특성 저하의 문제가 있고, 또, 양극활물질의 표면을 코팅하는 경우에는 활물질층내 도전 네트워크의 연결이 약해 사이클 특성 및 저장 안정성이 저하되는 문제가 있다. 이에 반해 본 발명의 일 실시예에 따른 양극은 양극활물질층내 전체에 걸쳐 도전성 네트워크가 균일하고 안정적으로 형성됨으로써, 전극내 전하 전달 저항이 크게 감소되고, 안정적으로 개선된 출력특성을 나타낼 수 있다. 또, 본 발명의 일 실시예에 따른 양극은 상기 구조체내 기공도 제어를 통해 양극활물질층내로의 물질 전달 저항 증가를 방지할 수 있다. That is, in the anode of the present invention manufactured according to the above method, a conductive layer including a porous mesh structure of carbon nanotubes is positioned on the anode active material layer, and the carbon nanotubes in the conductive layer are connected to the carbon nanotubes in the anode active material layer. By forming a conductive path, a significant improvement in resistance is reduced when using the same amount of carbon nanotubes compared with the case of mixing and using carbon nanotubes in the formation of the positive electrode active material layer and coating the surface of the positive electrode active material with carbon nanotubes. As a result, the battery output characteristics may be improved. In detail, when carbon nanotubes are mixed in the formation of the positive electrode active material layer, there is a problem of decreasing the probability of contact with the positive electrode active material and thus deteriorating battery characteristics by reducing the content of carbon nanotubes on the surface of the active material layer. In the case of coating the surface of the active material, there is a problem in that the connection of the conductive network in the active material layer is weak and the cycle characteristics and storage stability are lowered. In contrast, the anode according to the exemplary embodiment of the present invention has a uniform and stable conductive network formed throughout the cathode active material layer, thereby greatly reducing the charge transfer resistance in the electrode and stably improving output characteristics. In addition, the anode according to an embodiment of the present invention can prevent an increase in mass transfer resistance into the cathode active material layer through porosity control in the structure.
본 발명의 또 다른 일 실시예에 따르면, 상기 양극을 포함하는 전기화학소자가 제공된다. 상기 전기화학소자는 구체적으로 전지, 커패시터 등일 수 있으며, 보다 구체적으로는 리튬 이차전지일 수 있다.According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.
상기 리튬 이차전지는 구체적으로 양극, 상기 양극과 대향하여 위치하는 음극, 상기 양극과 음극 사이에 개재되는 세퍼레이터 및 전해질을 포함하며, 상기 양극은 앞서 설명한 바와 같다. 또, 상기 리튬 이차전지는 상기 양극, 음극, 세퍼레이터의 전극 조립체를 수납하는 전지용기, 및 상기 전지용기를 밀봉하는 밀봉 부재를 선택적으로 더 포함할 수 있다. The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. The lithium secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.
상기 리튬 이차전지에 있어서, 상기 음극은 음극집전체 및 상기 음극집전체 상에 위치하는 음극활물질층을 포함한다.In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.
상기 음극집전체는 전지에 화학적 변화를 유발하지 않으면서 높은 도전성을 가지는 것이라면 특별히 제한되는 것은 아니며, 예를 들어, 구리, 스테인레스 스틸, 알루미늄, 니켈, 티탄, 소성 탄소, 구리나 스테인레스 스틸의 표면에 탄소, 니켈, 티탄, 은 등으로 표면처리한 것, 알루미늄-카드뮴 합금 등이 사용될 수 있다. 또, 상기 음극 집전체는 통상적으로 3 내지 500㎛의 두께를 가질 수 있으며, 양극 집전체와 마찬가지로, 상기 집전체 표면에 미세한 요철을 형성하여 음극활물질의 결합력을 강화시킬 수도 있다. 예를 들어, 필름, 시트, 호일, 네트, 다공질체, 발포체, 부직포체 등 다양한 형태로 사용될 수 있다.The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on a surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of about 3 to 500 μm, and like the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.
상기 음극활물질층은 음극활물질과 함께 선택적으로 바인더 및 도전재를 포함한다. 상기 음극활물질층은 일례로서 음극집전체 상에 음극활물질, 및 선택적으로 바인더 및 도전재를 포함하는 음극 형성용 조성물을 도포하고 건조하거나, 또는 상기 음극 형성용 조성물을 별도의 지지체 상에 캐스팅한 다음, 이 지지체로부터 박리하여 얻은 필름을 음극집전체 상에 라미네이션함으로써 제조될 수도 있다.The negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material. For example, the negative electrode active material layer is coated with a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material on a negative electrode current collector and dried, or casting the negative electrode forming composition on a separate support It may be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.
상기 음극활물질로는 리튬의 가역적인 인터칼레이션 및 디인터칼레이션이 가능한 화합물이 사용될 수 있다. 구체적인 예로는 인조흑연, 천연흑연, 흑연화 탄소섬유, 비정질탄소 등의 탄소질 재료; Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si합금, Sn합금 또는 Al합금 등 리튬과 합금화가 가능한 금속질 화합물; SiOx(0 < x < 2), SnO2, 바나듐 산화물, 리튬 바나듐 산화물과 같이 리튬을 도프 및 탈도프할 수 있는 금속산화물; 또는 Si-C 복합체 또는 Sn-C 복합체와 같이 상기 금속질 화합물과 탄소질 재료를 포함하는 복합물 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다. 또한, 상기 음극활물질로서 금속 리튬 박막이 사용될 수도 있다. 또, 탄소재료는 저결정 탄소 및 고결정성 탄소 등이 모두 사용될 수 있다. 저결정성 탄소로는 연화탄소 (soft carbon) 및 경화탄소 (hard carbon)가 대표적이며, 고결정성 탄소로는 무정형, 판상, 인편상, 구형 또는 섬유형의 천연 흑연 또는 인조 흑연, 키시흑연 (Kish graphite), 열분해 탄소 (pyrolytic carbon), 액정피치계 탄소섬유 (mesophase pitch based carbon fiber), 탄소 미소구체 (meso-carbon microbeads), 액정피치 (Mesophase pitches) 및 석유와 석탄계 코크스 (petroleum or coal tar pitch derived cokes) 등의 고온 소성탄소가 대표적이다.As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; Metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides capable of doping and undoping lithium such as SiO x (0 <x <2), SnO 2 , vanadium oxide, lithium vanadium oxide; Or a composite including the metallic compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is typical.
또, 상기 바인더 및 도전재는 앞서 양극에서 설명한 바와 동일한 것일 수 있다.In addition, the binder and the conductive material may be the same as described above in the positive electrode.
한편, 상기 리튬 이차전지에 있어서, 세퍼레이터는 음극과 양극을 분리하고 리튬 이온의 이동 통로를 제공하는 것으로, 통상 리튬 이차전지에서 세퍼레이터로 사용되는 것이라면 특별한 제한없이 사용가능하며, 특히 전해질의 이온 이동에 대하여 저저항이면서 전해액 함습 능력이 우수한 것이 바람직하다. 구체적으로는 다공성 고분자 필름, 예를 들어 에틸렌 단독중합체, 프로필렌 단독중합체, 에틸렌/부텐 공중합체, 에틸렌/헥센 공중합체 및 에틸렌/메타크릴레이트 공중합체 등과 같은 폴리올레핀계 고분자로 제조한 다공성 고분자 필름 또는 이들의 2층 이상의 적층 구조체가 사용될 수 있다. 또 통상적인 다공성 부직포, 예를 들어 고융점의 유리 섬유, 폴리에틸렌테레프탈레이트 섬유 등으로 된 부직포가 사용될 수도 있다. 또, 내열성 또는 기계적 강도 확보를 위해 세라믹 성분 또는 고분자 물질이 포함된 코팅된 세퍼레이터가 사용될 수도 있으며, 선택적으로 단층 또는 다층 구조로 사용될 수 있다.On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular to the ion movement of the electrolyte It is desirable to have a low resistance against the electrolyte and excellent electrolytic solution-moisture capability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.
또, 본 발명에서 사용되는 전해질로는 리튬 이차전지 제조시 사용 가능한 유기계 액체 전해질, 무기계 액체 전해질, 고체 고분자 전해질, 겔형 고분자 전해질, 고체 무기 전해질, 용융형 무기 전해질 등을 들 수 있으며, 이들로 한정되는 것은 아니다. In addition, examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.
구체적으로, 상기 전해질은 유기 용매 및 리튬염을 포함할 수 있다. Specifically, the electrolyte may include an organic solvent and a lithium salt.
상기 유기 용매로는 전지의 전기 화학적 반응에 관여하는 이온들이 이동할 수 있는 매질 역할을 할 수 있는 것이라면 특별한 제한없이 사용될 수 있다. 구체적으로 상기 유기 용매로는, 메틸 아세테이트(methyl acetate), 에틸 아세테이트(ethyl acetate), γ-부티로락톤(γ-butyrolactone), ε-카프로락톤(ε-caprolactone) 등의 에스테르계 용매; 디부틸 에테르(dibutyl ether) 또는 테트라히드로퓨란(tetrahydrofuran) 등의 에테르계 용매; 시클로헥사논(cyclohexanone) 등의 케톤계 용매; 벤젠(benzene), 플루오로벤젠(fluorobenzene) 등의 방향족 탄화수소계 용매; 디메틸카보네이트(dimethylcarbonate, DMC), 디에틸카보네이트(diethylcarbonate, DEC), 메틸에틸카보네이트(methylethylcarbonate, MEC), 에틸메틸카보네이트(ethylmethylcarbonate, EMC), 에틸렌카보네이트(ethylene carbonate, EC), 프로필렌카보네이트(propylene carbonate, PC) 등의 카보네이트계 용매; 에틸알코올, 이소프로필 알코올 등의 알코올계 용매; R-CN(R은 C2 내지 C20의 직쇄상, 분지상 또는 환 구조의 탄화수소기이며, 이중결합 방향 환 또는 에테르 결합을 포함할 수 있다) 등의 니트릴류; 디메틸포름아미드 등의 아미드류; 1,3-디옥솔란 등의 디옥솔란류; 또는 설포란(sulfolane)류 등이 사용될 수 있다. 이중에서도 카보네이트계 용매가 바람직하고, 전지의 충방전 성능을 높일 수 있는 높은 이온전도도 및 고유전율을 갖는 환형 카보네이트(예를 들면, 에틸렌카보네이트 또는 프로필렌카보네이트 등)와, 저점도의 선형 카보네이트계 화합물(예를 들면, 에틸메틸카보네이트, 디메틸카보네이트 또는 디에틸카보네이트 등)의 혼합물이 보다 바람직하다. 이 경우 환형 카보네이트와 사슬형 카보네이트는 약 1:1 내지 약 1:9의 부피비로 혼합하여 사용하는 것이 전해액의 성능이 우수하게 나타날 수 있다. The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of about 1: 1 to about 1: 9, so that the performance of the electrolyte may be excellent.
상기 리튬염은 리튬 이차전지에서 사용되는 리튬 이온을 제공할 수 있는 화합물이라면 특별한 제한없이 사용될 수 있다. 구체적으로 상기 리튬염은, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, 또는 LiB(C2O4)2 등이 사용될 수 있다. 상기 리튬염의 농도는 0.1 내지 2.0M 범위 내에서 사용하는 것이 좋다. 리튬염의 농도가 상기 범위에 포함되면, 전해질이 적절한 전도도 및 점도를 가지므로 우수한 전해질 성능을 나타낼 수 있고, 리튬 이온이 효과적으로 이동할 수 있다.The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAl0 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN (C 2 F 5 SO 3 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN (CF 3 SO 2 ) 2 . LiCl, LiI, or LiB (C 2 O 4 ) 2 and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.
상기 전해질에는 상기 전해질 구성 성분들 외에도 전지의 수명특성 향상, 전지 용량 감소 억제, 전지의 방전 용량 향상 등을 목적으로 예를 들어, 디플루오로 에틸렌카보네이트 등과 같은 할로알킬렌카보네이트계 화합물, 피리딘, 트리에틸포스파이트, 트리에탄올아민, 환상 에테르, 에틸렌 디아민, n-글라임(glyme), 헥사인산 트리아미드, 니트로벤젠 유도체, 유황, 퀴논 이민 염료, N-치환 옥사졸리디논, N,N-치환 이미다졸리딘, 에틸렌 글리콜 디알킬 에테르, 암모늄염, 피롤, 2-메톡시 에탄올 또는 삼염화 알루미늄 등의 첨가제가 1종 이상 더 포함될 수도 있다. 이때 상기 첨가제는 전해질 총 중량에 대하여 0.1 내지 5 중량%로 포함될 수 있다. In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, tri, etc. for the purpose of improving battery life characteristics, reducing battery capacity, and improving discharge capacity of the battery. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be included. In this case, the additive may be included in 0.1 to 5% by weight based on the total weight of the electrolyte.
상기와 같이 본 발명에 따른 양극활물질을 포함하는 리튬 이차전지는 우수한 방전 용량, 출력 특성 및 용량 유지율을 안정적으로 나타내기 때문에, 휴대전화, 노트북 컴퓨터, 디지털 카메라 등의 휴대용 기기, 및 하이브리드 전기자동차(hybrid electric vehicle, HEV) 등의 전기 자동차 분야 등에 유용하다. As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicle fields such as hybrid electric vehicle (HEV).
이에 따라, 본 발명의 다른 일 구현예에 따르면, 상기 리튬 이차전지를 단위 셀로 포함하는 전지 모듈 및 이를 포함하는 전지팩이 제공된다. Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.
상기 전지모듈 또는 전지팩은 파워 툴(Power Tool); 전기자동차(Electric Vehicle, EV), 하이브리드 전기자동차, 및 플러그인 하이브리드 전기자동차(Plug-in Hybrid Electric Vehicle, PHEV)를 포함하는 전기차; 또는 전력 저장용 시스템 중 어느 하나 이상의 중대형 디바이스 전원으로 이용될 수 있다.The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.
이하, 본 발명이 속하는 기술 분야에서 통상의 지식을 가진 자가 용이하게 실시할 수 있도록 본 발명의 실시예에 대하여 상세히 설명한다. 그러나 본 발명은 여러 가지 상이한 형태로 구현될 수 있으며 여기에서 설명하는 실시예에 한정되지 않는다. Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.
실시예Example
이하 실시예 및 비교예에서의 양극활물질층 및 도전층의 기공도는 하기 수학식 1 및 2에 따라 각각 결정하였으며, 각각의 물질의 진밀도를 기준으로 부피로 환산하고, 원하는 기공도에 해당하는 두께로 전극을 압연하여 조절하였다. The porosity of the positive electrode active material layer and the conductive layer in the following Examples and Comparative Examples were determined in accordance with the following equations (1) and (2), respectively, converted to volume based on the true density of each material, corresponding to the desired porosity The thickness was adjusted by rolling the electrode.
[수학식 1][Equation 1]
Figure PCTKR2016014002-appb-I000003
Figure PCTKR2016014002-appb-I000003
상기 식에서, 샘플 부피는 25cm2 X 양극활물질층의 두께이다.Wherein the sample volume is the thickness of the 25 cm 2 X cathode active material layer.
[수학식 2][Equation 2]
Figure PCTKR2016014002-appb-I000004
Figure PCTKR2016014002-appb-I000004
상기 식에서, 도전층 부피는 25cm2 X 도전층의 두께이다.Wherein the conductive layer volume is the thickness of the 25 cm 2 X conductive layer.
실시예 1Example 1
(양극 집전체 제조)(Positive current collector manufacturing)
Li(Ni0.6Mn0.2Co0.2)O2 양극활물질(D50=11㎛), 제1 탄소나노튜브(단위체의 길이: 3㎛, 직경: 10nm, 비표면적: 300m2/g, 벌크밀도: 0.13kg/m3의 번들형 탄소 나노튜브) 및 PVdF 바인더를 98.02 : 0.4 : 1.58의 중량 비율로 N-메틸피롤리돈 용매 중에서 혼합하여 양극 형성용 조성물(점도: 5000mPa·s)을 제조하고, 이를 알루미늄 집전체에 도포한 후, 130℃에서 건조하여 양극조립체를 제조하였다(양극활물질층의 기공도: 30부피%). Li (Ni 0.6 Mn 0.2 Co 0.2 ) O 2 cathode active material (D 50 = 11㎛), first carbon nanotube (unit length: 3㎛, diameter: 10nm, specific surface area: 300m 2 / g, bulk density: 0.13 kg / m 3 bundled carbon nanotubes) and PVdF binder were mixed in an N-methylpyrrolidone solvent at a weight ratio of 98.02: 0.4: 1.58 to prepare a composition for forming an anode (viscosity: 5000 mPa · s). After coating the aluminum current collector, it was dried at 130 ° C to prepare a positive electrode assembly (porosity of the positive electrode active material layer: 30% by volume).
(도전층 형성용 조성물 제조)(Manufacture of composition for conductive layer formation)
제2 탄소 나노튜브(단위체의 길이: 5㎛, 직경: 10nm, 비표면적: 300m2/g, 벌크밀도: 0.13kg/m3의 번들형 탄소 나노튜브) 0.05g을 이소프로필 알코올 100ml 표면에 천천히 적하한 다음, 10분 동안 초음파 분산을 실시하여 이소프로필 알코올 표면에 제2 탄소 나노튜브로 이루어진 3차원 다공성 망상 구조체를 포함하는 막이 형성된 도전층 형성용 조성물을 제조하였다.0.05 g of second carbon nanotubes (unit length: 5 μm, diameter: 10 nm, specific surface area: 300 m 2 / g, bulk density: 0.13 kg / m 3 in bundle carbon nanotubes) were slowly added to the surface of 100 ml of isopropyl alcohol. After dropping, ultrasonic dispersion was performed for 10 minutes to prepare a composition for forming a conductive layer on which a film including a three-dimensional porous network structure composed of second carbon nanotubes was formed on the surface of isopropyl alcohol.
(도전층 제조)(Conductive layer manufacturing)
상기 제조된 양극조립체를 상기 도전층 형성용 조성물에 30초 동안 함침시킨 후, 상기 제2 탄소 나노튜브 막이 양극활물질층 표면 상에 위치하도록 전극 조립체를 0.15 m/min의 속도로 3초 동안 가만히 들어올리고, 10 Pa, 80℃, 6 시간 건조하여 양극활물질층 표면에 도전층이 형성된 양극을 제조하였다 (양극활물질층 대비 도전층의 두께비 = 1:0.002, 활물질층 기공도 = 30 부피%, 도전층 기공도 = 56 부피%, 제1 탄소나노튜브 : 제2 탄소 나노튜브의 중량비 = 1 : 0.17 (도 3 참조)(하기 표 1 참조).After impregnating the prepared cathode assembly into the composition for forming a conductive layer for 30 seconds, the electrode assembly was gently lifted for 3 seconds at a rate of 0.15 m / min so that the second carbon nanotube film was positioned on the surface of the cathode active material layer. Oligo, dried at 10 Pa, 80 ° C. for 6 hours to prepare a positive electrode having a conductive layer on the surface of the positive electrode active material layer (thickness ratio of the conductive layer to the positive electrode active material layer = 1: 0.002, porosity of the active material layer = 30% by volume, conductive layer Porosity = 56% by volume, weight ratio of the first carbon nanotubes to the second carbon nanotubes = 1: 0.17 (see FIG. 3) (see Table 1 below).
실시예 2 Example 2
상기 실시예 1의 양극 집전체 제조 시에, Li(Ni0.6Mn0.2Co0.2)O2 양극활물질(D50=11㎛), 제1 탄소 나노튜브(단위체의 길이: 3㎛, 직경: 10nm, 비표면적: 300m2/g, 벌크밀도: 0.13kg/m3의 번들형 탄소 나노튜브) 및 PVdF 바인더를 98.26 : 0.2 : 1.54의 중량비로 N-메틸피롤리돈 용매 중에서 혼합하여 제조한 양극 형성용 조성물(점도: 5000mPa·s)을 사용하는 것을 제외하고는, 상기 실시예 1에서와 동일한 방법으로 수행하여 양극을 제조하였다(양극활물질층 대비 도전층의 두께비 = 1:0.002, 활물질층내 기공도 = 30 부피%, 도전층의 기공도 = 56 부피%, 제1 탄소나노튜브 : 제2 탄소 나노튜브의 중량비 = 1 : 0.34) (하기 표 1 참조).In preparing the positive electrode current collector of Example 1, a Li (Ni 0.6 Mn 0.2 Co 0.2 ) O 2 cathode active material (D 50 = 11 μm), a first carbon nanotube (unit length: 3 μm, diameter: 10 nm, Specific surface area: 300 m 2 / g, bulk density: 0.13 kg / m 3 of bundled carbon nanotubes) and PVdF binders in a N-methylpyrrolidone solvent at a weight ratio of 98.26: 0.2: 1.54 Except for using the composition (viscosity: 5000mPa · s), the positive electrode was prepared in the same manner as in Example 1 (thickness ratio of the conductive layer to the positive electrode active material layer = 1: 0.002, porosity in the active material layer = 30% by volume, porosity of the conductive layer = 56% by volume, weight ratio of the first carbon nanotubes to the second carbon nanotubes = 1: 0.34) (see Table 1 below).
실시예 3 Example 3
상기 실시예 1의 도전층 형성용 조성물 제조 시에 제2 탄소 나노튜브(단위체의 길이: 7㎛, 직경: 9nm, 비표면적: 300m2/g, 벌크밀도: 0.13kg/m3의 번들형 탄소 나노튜브) 0.9g을 이소프로필 알코올 100ml 표면에 천천히 적하한 다음, 10분 동안 초음파 분산을 실시하여 이소프로필 알코올 표면에 제2 탄소 나노튜브로 이루어진 3차원 다공성 망상 구조체를 포함하는 막이 형성된 도전층 형성용 조성물을 제조하였다. 사용하는 것을 제외하고는, 상기 실시예 1에서와 동일한 방법으로 수행하여 양극을 제조하였다 (양극활물질층 대비 도전층의 두께비=1:0.005, 활물질층내 기공도 = 30 부피%, 도전층의 기공도 = 56 부피%, 제1 탄소나노튜브 : 제2 탄소 나노튜브의 중량비 = 1 : 0.42) (하기 표 1 참조).Second carbon nanotubes (length of unit: 7 μm, diameter: 9 nm, specific surface area: 300 m 2 / g, bulk density: 0.13 kg / m 3) when preparing the composition for forming a conductive layer of Example 1 Nanotube) 0.9g was slowly added to the surface of 100ml isopropyl alcohol, and then ultrasonically dispersed for 10 minutes to form a conductive layer having a film including a three-dimensional porous network structure composed of second carbon nanotubes on the surface of isopropyl alcohol. A composition for preparation was prepared. Except for using, the positive electrode was manufactured by the same method as in Example 1 (thickness ratio of the conductive layer to the positive electrode active material layer = 1: 0.005, porosity in the active material layer = 30% by volume, porosity of the conductive layer) = 56% by volume, weight ratio of the first carbon nanotubes to the second carbon nanotubes = 1: 0.42) (see Table 1 below).
실시예 4 Example 4
상기 실시예 1의 도전층 형성용 조성물 제조 시에 제2 탄소 나노튜브(단위체의 길이: 3㎛, 직경: 10nm, 비표면적: 300m2/g, 벌크밀도: 0.13kg/m3의 번들형 탄소 나노튜브) 0.5g을 이소프로필 알코올 100ml 표면에 천천히 적하한 다음, 10분 동안 초음파 분산을 실시하여 이소프로필 알코올 표면에 제2 탄소 나노튜브로 이루어진 3차원 다공성 망상 구조체를 포함하는 막이 형성된 도전층 형성용 조성물을 사용하는 것을 제외하고는, 상기 실시예 1에서와 동일한 방법으로 수행하여 양극을 제조하였다 (양극활물질층 대비 도전층의 두께비 = 1:0.001, 활물질층내 기공도 = 30 부피%, 도전층의 기공도 = 56 부피%, 제1 탄소나노튜브 : 제2 탄소 나노튜브의 중량비 = 1 : 0.08) (하기 표 1 참조).Second carbon nanotubes (length of the unit: 3 μm, diameter: 10 nm, specific surface area: 300 m 2 / g, bulk density: 0.13 kg / m 3) when manufacturing the composition for forming a conductive layer of Example 1 0.5g) is slowly added dropwise to 100ml surface of isopropyl alcohol, and then ultrasonically dispersed for 10 minutes to form a conductive layer having a film including a three-dimensional porous network structure composed of second carbon nanotubes on the surface of isopropyl alcohol. Except for using the composition, the positive electrode was prepared in the same manner as in Example 1 (thickness ratio of the conductive layer to the positive electrode active material layer = 1: 0.001, porosity in the active material layer = 30% by volume, conductive layer Porosity = 56% by volume, weight ratio of the first carbon nanotubes to the second carbon nanotubes = 1: 0.08) (see Table 1 below).
비교예 1 Comparative Example 1
상기 실시예 1에서 양극활물질층 표면상에 도전층을 형성하지 않는 것을 제외하고는 상기 실시예 1에서와 동일한 방법으로 수행하여 양극을 제조하였다(하기 표 1 참조). Except not forming a conductive layer on the surface of the positive electrode active material layer in Example 1 was prepared in the same manner as in Example 1 to prepare a positive electrode (see Table 1 below).
비교예 2Comparative Example 2
상기 실시예 1에서 도전층 형성시 도전층의 기공도를 35%로 낮춘 것을 제외하고는 상기 실시예 1에서와 동일한 방법으로 수행하여 양극을 제조하였다(양극활물질층 대비 도전층의 두께비 = 1:0.002, 활물질층내 기공도 = 30 부피%, 도전층의 기공도 = 35 부피%, 제1 탄소나노튜브 : 제2 탄소 나노튜브의 중량비 = 1 : 0.1) (하기 표 1 참조).Except for lowering the porosity of the conductive layer to 35% when forming the conductive layer in Example 1 was prepared in the same manner as in Example 1 to prepare a positive electrode (thickness ratio of the conductive layer to the positive electrode active material layer = 1: 0.002, porosity in the active material layer = 30% by volume, porosity in the conductive layer = 35% by volume, weight ratio of the first carbon nanotubes to the second carbon nanotubes = 1: 0.1) (see Table 1 below).
비교예 3Comparative Example 3
상기 실시예 1에서 도전층 형성시 탄소나노튜브의 함량을 양극활물질층 대비 0.056 비율로 높여 도전층 내 기공도와 양극활물질층내 기공도와의 차이가 거의 없도록 하는 것을 제외하고는 상기 실시예 1에서와 동일한 방법으로 수행하여 양극을 제조하였다(양극활물질층 대비 도전층의 두께비 = 1:0.056, 활물질층내 기공도 = 30 부피%, 도전층의 기공도 = 30 부피%, 제1 탄소나노튜브 : 제2 탄소 나노튜브의 중량비 = 1 :4.7) (하기 표 1 참조).When forming the conductive layer in Example 1, the carbon nanotube content is increased to a ratio of 0.056 relative to the positive electrode active material layer so that there is little difference between the porosity in the conductive layer and the porosity in the positive electrode active material layer. A positive electrode was prepared by the method (thickness ratio of the conductive layer to the positive electrode active material layer = 1: 0.056, porosity in the active material layer = 30% by volume, porosity in the conductive layer = 30% by volume, first carbon nanotube: second carbon). Weight ratio of nanotubes = 1: 4.7) (see Table 1 below).
비교예 4Comparative Example 4
상기 실시예 2에서 양극활물질층 표면 상에 도전층을 형성하지 않은 것을 제외하고는 상기 실시예 2에서와 동일한 방법으로 수행하여 양극을 제조하였다 (양극활물질층내 기공도 = 30 부피%)(하기 표 1 참조).Except not forming a conductive layer on the surface of the positive electrode active material layer in Example 2 was prepared in the same manner as in Example 2 to prepare a positive electrode (porosity in the positive electrode active material layer = 30% by volume) (Table below) 1).
참고예Reference Example
(도전층 형성용 조성물 제조)(Manufacture of composition for conductive layer formation)
제2 탄소 나노튜브(단위체의 길이: 5㎛, 직경: 10nm, 비표면적: 300m2/g, 벌크밀도: 0.13kg/m3의 번들형 탄소 나노튜브) 0.05g을 이소프로필 알코올 100ml에 혼합하여 도전층 형성용 조성물을 제조하였다.0.05 g of the second carbon nanotubes (unit length: 5 µm, diameter: 10 nm, specific surface area: 300 m 2 / g, bulk density: 0.13 kg / m 3 in bundle carbon nanotubes) was mixed with 100 ml of isopropyl alcohol. A composition for forming a conductive layer was prepared.
(도전층 제조) (Conductive layer manufacturing)
상기 실시예 1에서 제조된 양극조립체 표면에 상기 도전층 형성용 조성물을 직접 도포한 후, 건조하여 도전층을 표면에 코팅된 양극을 제조하였다(도 5 참조) (양극활물질층 대비 도전층의 두께비 = 1:0.02, 활물질층내 기공도 = 30 부피%, 도전층의 기공도 = 54 부피%, 제1 탄소나노튜브 : 제2 탄소 나노튜브의 중량비 = 1 : 1.6) (하기 표 1 참조).The composition for forming the conductive layer was directly applied to the surface of the cathode assembly prepared in Example 1, and then dried to prepare a cathode coated on the surface of the conductive layer (see FIG. 5) (thickness ratio of the conductive layer to the positive electrode active material layer). = 1: 0.02, porosity in the active material layer = 30% by volume, porosity of the conductive layer = 54% by volume, weight ratio of the first carbon nanotubes to the second carbon nanotubes = 1: 1.6) (see Table 1 below).
양극활물질층의 기공도 - 도전층의 기공도 차이(부피%)Porosity of Anode Active Material Layer-Difference in Porosity of Conductive Layer (Volume%) 양극활물질층:도전층 두께비Cathode active material layer: conductive layer thickness ratio 제1 탄소나노튜브:제2 탄소나노튜브의 중량비First Carbon Nanotube: Weight Ratio of Second Carbon Nanotube
실시예1Example 1 2626 1:0.0021: 0.002 1:0.171: 0.17
실시예2Example 2 2626 1:0.0021: 0.002 1:0.341: 0.34
실시예3Example 3 2626 1:0.0051: 0.005 1:0.421: 0.42
실시예4Example 4 2626 1:0.0011: 0.001 1:0.081: 0.08
비교예1Comparative Example 1 -- -- --
비교예2Comparative Example 2 55 1:0.0021: 0.002 1:0.11: 0.1
비교예3Comparative Example 3 00 1:0.0561: 0.056 1:4.71: 4.7
비교예4Comparative Example 4 -- -- --
참고예Reference Example 2424 1:0.021: 0.02 1:1.61: 1.6
제조예: 리튬 이차전지의 제조Preparation Example: Fabrication of Lithium Secondary Battery
상기 실시예 1 내지 4, 비교예 1 내지 4 및 참고예에서 제조한 양극을 이용하여 리튬 이차전지를 각각 제조하였다.Lithium secondary batteries were prepared using the positive electrodes prepared in Examples 1 to 4, Comparative Examples 1 to 4, and Reference Examples, respectively.
상세하게는 음극활물질로서 천연흑연, 카본블랙 도전재, SBR 바인더 및 카르복시메틸셀룰로오스(CMC)를 N-메틸피롤리돈 용매 중에서 중량비로 96:1:2:1의 비율로 혼합하여 음극 형성용 조성물을 제조하고, 이를 구리 집전체에 도포하여 음극을 제조하였다.In detail, as a negative electrode active material, a natural graphite, a carbon black conductive material, an SBR binder, and carboxymethyl cellulose (CMC) are mixed in an N-methylpyrrolidone solvent in a weight ratio of 96: 1: 2: 1 to form a negative electrode. Was prepared and applied to a copper current collector to prepare a negative electrode.
상기 실시예 1 내지 4, 비교예 1 내지 4 및 참고예에서 제조한 각각의 양극과, 상기에서 제조한 음극 사이에 다공성 폴리에틸렌의 세퍼레이터를 개재하여 전극 조립체를 제조하고, 상기 전극 조립체를 케이스 내부에 위치시킨 후, 케이스 내부로 전해액을 주입하여 리튬 이차 전지를 제조하였다. 이때 전해액은 에틸렌카보네이트/디메틸카보네이트/에틸메틸카보네이트(EC/DMC/EMC의 혼합 부피비 = 3/4/3)로 이루어진 유기 용매에 1.0M 농도의 리튬 헥사플루오로포스페이트(LiPF6)를 용해시켜 제조하였다.An electrode assembly was manufactured by interposing a separator of porous polyethylene between each of the positive electrodes prepared in Examples 1 to 4, Comparative Examples 1 to 4, and the reference example, and the negative electrode prepared above, and the electrode assembly was placed inside the case. After positioning, an electrolyte was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte is prepared by dissolving 1.0M concentration of lithium hexafluorophosphate (LiPF 6 ) in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3/4/3). It was.
실험예Experimental Example
실험예 1: 율 특성 평가Experimental Example 1: Evaluation of rate characteristics
상기 실시예 1 내지 4, 비교예 1 내지 4 및 참고예에서 제조한 각각의 양극을 이용하여 제조한 코인셀(Li 금속의 음극 사용)을 25℃에서 0.1C의 정전류(CC) 4.25V가 될 때까지 충전하고, 이후 4.25V의 정전압(CV)으로 충전하여 충전 전류가 0.05mAh가 될 때까지 1회째 충전을 행하였다. 이후 20분간 방치한 다음 0.1C의 정전류로 3.0V가 될 때까지 방전하여 1 사이클째의 방전 용량을 측정하였다. 이후 2C로 방전 조건을 달리하여 율 특성을 평가하였다. 그 결과를 하기 도 6에 나타내었다.Coin cells (using a negative electrode of Li metal) prepared by using the respective anodes prepared in Examples 1 to 4, Comparative Examples 1 to 4, and Reference Examples were to have a constant current (CC) of 4.25V at 25 ° C. The battery was charged until then, and then charged at a constant voltage (CV) of 4.25V to perform a first charge until the charging current became 0.05 mAh. After standing for 20 minutes, the battery was discharged to a constant current of 0.1C until 3.0V, and the discharge capacity of the first cycle was measured. Then, rate characteristics were evaluated by varying the discharge conditions at 2C. The results are shown in FIG. 6.
실험결과, 실시예 1 내지 4의 양극은 도전층을 형성하지 않은 비교예 1 및 4의 양극, 그리고 도전층내 기공도와 양극활물질층내 기공도의 차이가 10 부피% 미만으로 작은 비교예 2, 도전층 내 탄소나노튜브가 지나치게 과량으로 포함된 비교예 3의 양극에 비해 우수한 율 특성을 나타내었다. As a result, the anodes of Examples 1 to 4 are the anodes of Comparative Examples 1 and 4 that do not form a conductive layer, and Comparative Example 2, the conductive layer having a small difference in porosity in the conductive layer and a porosity in the cathode active material layer is less than 10% by volume. Compared to the positive electrode of Comparative Example 3 in which excessive carbon nanotubes were included in an excessive amount, excellent rate characteristics were shown.
한편, 기존 코팅 방법을 사용하여 도전층 슬러리를 도포하여 형성한 참고예의 도전층을 포함하는 양극의 경우, 양극활물질층 대비 도전층의 두께비를 1:0.02 이하로 조절하기 어려울 뿐만 아니라, 양극활물질층 표면 전면에 도전층이 형성됨으로써, 전해액 내의 리튬 이온이 전극으로 이동하는 것이 원활하지 못하여, 율 특성이 실시예 1 내지 4의 양극 대비 저하되었다.On the other hand, in the case of the positive electrode including the conductive layer of the reference example formed by applying the conductive layer slurry using the existing coating method, it is difficult to control the thickness ratio of the conductive layer to the positive electrode active material layer to 1: 0.02 or less, and the positive electrode active material layer By forming the conductive layer on the entire surface of the surface, lithium ions in the electrolyte were not smoothly moved to the electrode, and the rate characteristic was lowered compared to the anodes of Examples 1 to 4.
상세하게는, 실시예 1의 양극은 동일한 특성의 양극활물질층은 포함하지만 도전층은 포함하지 않는 비교예 1의 양극에 비해 우수한 율 특성을 나타내었다. 이로부터 도전층의 형성을 통해 율 특성을 향상시킬 수 있음을 확인할 수 있다.In detail, the positive electrode of Example 1 exhibited excellent rate characteristics compared to the positive electrode of Comparative Example 1 including a positive electrode active material layer having the same characteristics but not containing a conductive layer. From this, it can be seen that the rate characteristic can be improved by forming the conductive layer.
또, 실시예 1의 양극은, 양극활물질층 및 도전층을 포함하지만 도전층과 양극활물질층 간의 기공도 차이가 10 부피% 미만인 비교예 2와, 도전층의 도전재가 너무 많아 두꺼운 도전층을 형성하는 비교예 3의 양극과 비교하여 우수한 율 특성을 나타내었다. 이는 도전층의 두께 또는 낮은 기공도로 인해 물질저항이 증가하였기 때문이다. In addition, the positive electrode of Example 1 includes a positive electrode active material layer and a conductive layer, but Comparative Example 2 having a porosity difference between the conductive layer and the positive electrode active material layer is less than 10% by volume, and the conductive material of the conductive layer is too large to form a thick conductive layer. Compared with the positive electrode of Comparative Example 3 showed excellent rate characteristics. This is because the material resistance is increased due to the thickness or low porosity of the conductive layer.
또, 실시예 2의 양극은 동일한 특성의 양극활물질층은 포함하지만 도전층은 포함하지 않는 비교예 4의 양극에 비해 우수한 율 특성을 나타내지만, 실시예 1의 양극에 비해서는 다소 낮은 율 특성을 나타내었다. 이는 실시예 2의 경우, 양극활물질층내 도전재의 함량이 실시예 1에 비해 감소됨으로써 활물질층내 도전 네트워크가 충분히 형성되지 않았기 때문이다.In addition, the positive electrode of Example 2 exhibits excellent rate characteristics compared to the positive electrode of Comparative Example 4, which includes a positive electrode active material layer having the same characteristics but does not include a conductive layer, but has a slightly lower rate characteristic than the positive electrode of Example 1. Indicated. This is because in the case of Example 2, the content of the conductive material in the positive electrode active material layer is reduced compared to Example 1, so that the conductive network in the active material layer is not sufficiently formed.
한편, 실시예 1 및 2의 양극은 도전층 슬러리를 도포하여 형성한 도전층을 포함하는 참고예의 양극에 비하여, 양극 활물질이 일부 노출된 망상 구조의 도전층이 형성되어 있기 때문에, 도전층내 물질 전달 저항 증가를 억제하여 높은 율 특성을 구현할 수 있다.On the other hand, since the positive electrode of Examples 1 and 2 has a network-like conductive layer in which the positive electrode active material is partially exposed, compared with the positive electrode of the reference example including the conductive layer formed by applying the conductive layer slurry, the material transfer in the conductive layer is performed. High rate characteristics can be realized by suppressing the increase in resistance.
실험예Experimental Example 2: 저항 특성 평가 2: resistance characteristic evaluation
상기 실시예 1 내지 4, 비교예 1 내지 4 및 참고예에서의 리튬 이차전지에 대해 하기와 같은 방법으로 저항 특성을 평가하였다. The resistance characteristics of the lithium secondary batteries of Examples 1 to 4, Comparative Examples 1 to 4, and Reference Examples were evaluated in the following manner.
상세하게는, 상온(25℃)에서 충방전한 전지를 SOC 50%를 기준으로 2.5C, 30초 동안 방전하여 저항을 측정한 후, 전위가변 EIS(potentiostat electrochemical impedance spectroscopy)를 이용하여 계면저항과 물질전달저항을 분리하여 측정하였다. 그 결과를 도 7에 나타내었다. Specifically, the battery charged and discharged at room temperature (25 ℃) for 2.5C, 30 seconds based on SOC 50% to measure the resistance, and then measured the resistance and the interface resistance using a potentiostat electrochemical impedance spectroscopy (EIS) The material transfer resistance was measured separately. The results are shown in FIG.
실험결과, 실시예 1 내지 4에서 제조한 리튬 이차전지의 경우 비교예 1 내지 4와 비교하여 계면저항이 크게 감소하여 우수한 출력을 나타냄을 할 수 있다. 특히 양극활물질층 위에 탄소나노튜브를 포함하는 도전층을 형성하여 표면측에 전기적 네트워크가 형성되도록 하여 계면저항을 크게 감소할 수 있다. 또한 비교예 2 및 3과, 참고예의 경우, 계면저항은 동등 수준이거나 크게 증가하지 않았으나, 도전층의 기공도를 제어함으로써 물질 전달 저항을 감소시킬 수 있음을 확인할 수 있다.As a result of the experiment, the lithium secondary batteries prepared in Examples 1 to 4 can significantly exhibit an excellent output as the interface resistance is greatly reduced compared to Comparative Examples 1 to 4. In particular, by forming a conductive layer including carbon nanotubes on the cathode active material layer to form an electrical network on the surface side it can significantly reduce the interface resistance. In addition, in the case of Comparative Examples 2 and 3 and the reference example, the interfacial resistance was not the same level or significantly increased, it can be seen that the mass transfer resistance can be reduced by controlling the porosity of the conductive layer.

Claims (13)

  1. 양극 집전체,Anode current collector,
    상기 양극 집전체의 표면 상에 위치하며, 양극활물질 및 제1 탄소나노튜브를 포함하는 다공성 양극활물질층, 및Located on the surface of the positive electrode current collector, a porous positive electrode active material layer comprising a positive electrode active material and a first carbon nanotube, and
    상기 양극활물질층이 표면 상에 위치하는 도전층을 포함하고,The cathode active material layer comprises a conductive layer located on the surface,
    상기 도전층은 복수 개의 제2 탄소나노튜브에 의해 형성된 다공성 망상 구조체를 포함하며, 양극활물질층의 기공도 + 10 부피% 이상의 기공도를 갖는 것인 이차전지용 양극.The conductive layer includes a porous network structure formed by a plurality of second carbon nanotubes, and has a porosity of the positive electrode active material layer + porosity of 10% by volume or more.
  2. 청구항 1에 있어서,The method according to claim 1,
    상기 다공성 양극활물질층의 기공도는 10 부피% 내지 50 부피%이고, The porosity of the porous cathode active material layer is 10% by volume to 50% by volume,
    상기 도전층의 기공도는 20 부피% 내지 60 부피%인 것인 이차전지용 양극.The porosity of the conductive layer is 20% by volume to 60% by volume of the positive electrode for secondary batteries.
  3. 청구항 1에 있어서,The method according to claim 1,
    상기 다공성 망상 구조체는 양극활물질층 내 제1 탄소나노튜브와 연결되어 전기적 도전 경로를 형성하는 것인 이차전지용 양극.The porous network structure is a secondary battery positive electrode that is connected to the first carbon nanotubes in the positive electrode active material layer to form an electrically conductive path.
  4. 청구항 1에 있어서,The method according to claim 1,
    상기 제1 및 제2 탄소 나노튜브는 각각 독립적으로 번들형 탄소 나노튜브인 것인 이차전지용 양극.Wherein the first and second carbon nanotubes are each independently a bundled carbon nanotubes positive electrode for a secondary battery.
  5. 청구항 1에 있어서,The method according to claim 1,
    상기 제1 및 제2 탄소 나노튜브는 각각 독립적으로 탄소 나노튜브 단위체의 직경이 10 nm 내지 100 nm이고, 길이가 3 ㎛ 내지 10 ㎛인 것인 이차전지용 양극. Each of the first and second carbon nanotubes independently has a diameter of 10 nm to 100 nm and a length of 3 μm to 10 μm of carbon nanotube units.
  6. 청구항 1에 있어서,The method according to claim 1,
    상기 제1 및 제2 탄소 나노튜브는 각각 독립적으로 비표면적이 20 m2/g 내지 2000 m2/g인 것인 이차전지용 양극.Each of the first and second carbon nanotubes independently has a specific surface area of 20 m 2 / g to 2000 m 2 / g.
  7. 청구항 1에 있어서,The method according to claim 1,
    상기 양극활물질의 평균 입자 직경(D50)이 3 ㎛ 내지 20 ㎛인 것인 이차전지용 양극.An average particle diameter (D 50 ) of the positive electrode active material is a secondary battery positive electrode of 3 ㎛ to 20 ㎛.
  8. 청구항 1에 있어서,The method according to claim 1,
    상기 양극활물질층 : 도전층의 두께비는 1:0.001 내지 1:0.05인 것인 이차전지용 양극.The positive electrode active material layer: the thickness ratio of the conductive layer is 1: 0.001 to 1: 0.05 secondary battery positive electrode.
  9. 청구항 8에 있어서,The method according to claim 8,
    상기 양극활물질층 : 도전층의 두께비는 1:0.001 내지 1:0.01인 것인 이차전지용 양극.The positive electrode active material layer: the thickness ratio of the conductive layer is 1: 0.001 to 1: 0.01 of the secondary battery positive electrode.
  10. 청구항 8에 있어서,The method according to claim 8,
    상기 양극활물질층 : 도전층의 두께비는 1:0.001 내지 1:0.005인 것인 이차전지용 양극.The positive electrode active material layer: the thickness ratio of the conductive layer is 1: 0.001 to 1: 0.005 secondary battery positive electrode.
  11. 청구항 1에 있어서,The method according to claim 1,
    상기 제1 탄소 나노튜브 : 제2 탄소 나노튜브의 중량비는 1:0.08 내지 1:0.42인 것인 이차전지용 양극.The weight ratio of the first carbon nanotubes to the second carbon nanotubes is 1: 0.08 to 1: 0.42.
  12. 제2 탄소 나노튜브를 분산매 중에 첨가하여 분산매의 표면 상에 제2 탄소 나노튜브 막이 형성된 도전층 형성용 조성물을 준비하는 단계; 및Adding a second carbon nanotube to the dispersion medium to prepare a composition for forming a conductive layer on which a second carbon nanotube film is formed on the surface of the dispersion medium; And
    양극 집전체의 적어도 일면에, 양극활물질 및 제1 탄소 나노튜브를 포함하는 양극활물질층이 형성된 전극 조립체를 상기 도전층 형성용 조성물에 함침한 후 상기 제2 탄소 나노튜브 막이 양극활물질층 표면 상에 위치하도록 전극 조립체를 들어올려 도전층을 형성하는 단계;를 포함하는, 청구항 1의 이차전지용 양극의 제조방법.After impregnating the electrode assembly having a positive electrode active material layer including a positive electrode active material and a first carbon nanotube on at least one surface of the positive electrode current collector in the conductive layer forming composition, the second carbon nanotube film is formed on the surface of the positive electrode active material layer. Lifting the electrode assembly to position to form a conductive layer; comprising, the method of manufacturing a positive electrode for a secondary battery of claim 1.
  13. 청구항 1 내지 청구항 11 중 어느 한 항에 따른 양극을 포함하는 리튬 이차전지.A lithium secondary battery comprising the positive electrode according to any one of claims 1 to 11.
PCT/KR2016/014002 2015-11-30 2016-11-30 Cathode for secondary battery and secondary battery comprising same WO2017095151A1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
CN201680052380.0A CN108028355B (en) 2015-11-30 2016-11-30 Positive electrode for secondary battery and secondary battery comprising same
US15/754,479 US11196051B2 (en) 2015-11-30 2016-11-30 Positive electrode for secondary battery and secondary battery including the same
EP16871047.3A EP3370279B1 (en) 2015-11-30 2016-11-30 Cathode for secondary battery and secondary battery comprising same
JP2018509517A JP6620221B2 (en) 2015-11-30 2016-11-30 Secondary battery positive electrode and secondary battery including the same

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
KR20150169150 2015-11-30
KR10-2015-0169150 2015-11-30
KR10-2016-0161525 2016-11-30
KR1020160161525A KR101938237B1 (en) 2015-11-30 2016-11-30 Positive electrode for secondary battery and secondary battery comprising the same

Publications (1)

Publication Number Publication Date
WO2017095151A1 true WO2017095151A1 (en) 2017-06-08

Family

ID=58797311

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/KR2016/014002 WO2017095151A1 (en) 2015-11-30 2016-11-30 Cathode for secondary battery and secondary battery comprising same

Country Status (1)

Country Link
WO (1) WO2017095151A1 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2684168C1 (en) * 2017-08-10 2019-04-04 Тойота Дзидося Кабусики Кайся Completely solid-state accumulator and anode
WO2019160391A1 (en) * 2018-02-19 2019-08-22 주식회사 엘지화학 Cathode and secondary battery comprising same cathode
US20200373559A1 (en) * 2018-02-19 2020-11-26 Lg Chem, Ltd. Positive Electrode and Secondary Battery Including the Positive Electrode
CN115312701A (en) * 2022-09-29 2022-11-08 比亚迪股份有限公司 Positive plate and lithium ion battery

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20050052266A (en) 2003-11-29 2005-06-02 삼성에스디아이 주식회사 Method of preparing positive active material for rechargeable lithium battery and positive active material for rechargeable lithium battery comprising the same
US20060134326A1 (en) * 2004-12-22 2006-06-22 Fuji Xerox Co., Ltd. Method for forming carbon nanotube thin film
JP5070680B2 (en) * 2005-03-31 2012-11-14 大日本印刷株式会社 Nonaqueous electrolyte secondary battery electrode plate, method for producing the same, and nonaqueous electrolyte secondary battery
KR101494435B1 (en) * 2008-01-15 2015-02-23 삼성전자주식회사 Electrode, Lithium battery, method for preparing electrode and composition for electrode coating
KR20150027027A (en) * 2012-05-31 2015-03-11 미쓰비시 마테리알 가부시키가이샤 Electrode for lithium-ion secondary battery, and lithium-ion secondary battery using said electrode
WO2015047042A1 (en) * 2013-09-30 2015-04-02 주식회사 엘지화학 Carbon nanotube having high specific surface area and method for manufacturing same

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20050052266A (en) 2003-11-29 2005-06-02 삼성에스디아이 주식회사 Method of preparing positive active material for rechargeable lithium battery and positive active material for rechargeable lithium battery comprising the same
US20060134326A1 (en) * 2004-12-22 2006-06-22 Fuji Xerox Co., Ltd. Method for forming carbon nanotube thin film
JP5070680B2 (en) * 2005-03-31 2012-11-14 大日本印刷株式会社 Nonaqueous electrolyte secondary battery electrode plate, method for producing the same, and nonaqueous electrolyte secondary battery
KR101494435B1 (en) * 2008-01-15 2015-02-23 삼성전자주식회사 Electrode, Lithium battery, method for preparing electrode and composition for electrode coating
KR20150027027A (en) * 2012-05-31 2015-03-11 미쓰비시 마테리알 가부시키가이샤 Electrode for lithium-ion secondary battery, and lithium-ion secondary battery using said electrode
WO2015047042A1 (en) * 2013-09-30 2015-04-02 주식회사 엘지화학 Carbon nanotube having high specific surface area and method for manufacturing same

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2684168C1 (en) * 2017-08-10 2019-04-04 Тойота Дзидося Кабусики Кайся Completely solid-state accumulator and anode
WO2019160391A1 (en) * 2018-02-19 2019-08-22 주식회사 엘지화학 Cathode and secondary battery comprising same cathode
US20200373559A1 (en) * 2018-02-19 2020-11-26 Lg Chem, Ltd. Positive Electrode and Secondary Battery Including the Positive Electrode
CN115312701A (en) * 2022-09-29 2022-11-08 比亚迪股份有限公司 Positive plate and lithium ion battery

Similar Documents

Publication Publication Date Title
WO2017111542A1 (en) Anode active material for lithium secondary battery and anode for lithium secondary battery including same
WO2020116858A1 (en) Positive electrode active material for rechargeable battery, production method therefor and rechargeable battery positive electrode comprising same
WO2021101188A1 (en) Anode and secondary battery comprising same
WO2021066560A1 (en) Positive electrode and secondary battery including same
WO2021080374A1 (en) Method for preparing positive electrode active material precursor and positive electrode active material precursor
WO2017095151A1 (en) Cathode for secondary battery and secondary battery comprising same
WO2021049918A1 (en) Positive electrode material for secondary battery and lithium secondary battery comprising same
WO2022031116A1 (en) Positive electrode active material precursor and method for preparing same
WO2021194260A1 (en) Method for manufacturing anode
WO2021153987A1 (en) Negative electrode active material, negative electrode comprising same, and secondary battery comprising same
WO2019147093A1 (en) Conductive material, electrode-forming slurry including same, electrode, and lithium secondary battery manufactured using same
WO2022149951A1 (en) Method for preparing cathode active material and cathode active material
WO2022119313A1 (en) Positive electrode active material precursor, method for manufacturing same, and positive electrode active material
WO2022182162A1 (en) Cathode active material, cathode comprising same, and secondary battery
WO2021029650A1 (en) Cathode for lithium secondary battery and lithium secondary battery comprising same
WO2021118144A1 (en) Anode active material, preparation method therefor, and anode and secondary battery each comprising same
WO2024063554A1 (en) Negative electrode composition, negative electrode for lithium secondary battery, comprising same, and lithium secondary battery comprising negative electrode
WO2024049200A1 (en) Cathode active material precursor, preparation method therefor, method for preparing cathode active material by using same, and cathode active material
WO2023018187A1 (en) Negative electrode active material, negative electrode including same, secondary battery including same and method for preparing negative electrode active material
WO2021235818A1 (en) Method for manufacturing secondary battery
WO2023224447A1 (en) Positive electrode active material precursor, method for preparing positive electrode active material by using same, and positive electrode active material
WO2022203401A1 (en) Positive electrode active material for lithium secondary battery, manufacturing method therefor, positive electrode for lithium secondary battery, comprising same, and lithium secondary battery
WO2022235047A1 (en) Positive electrode active material for lithium secondary battery, and positive electrode and lithium secondary battery comprising same
WO2023027504A1 (en) Positive electrode active material and method for producing positive electrode active material
WO2023140702A1 (en) Positive electrode and lithium secondary battery comprising same

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 16871047

Country of ref document: EP

Kind code of ref document: A1

ENP Entry into the national phase

Ref document number: 2018509517

Country of ref document: JP

Kind code of ref document: A

WWE Wipo information: entry into national phase

Ref document number: 15754479

Country of ref document: US

NENP Non-entry into the national phase

Ref country code: DE